Thank you t0xicCode for this patch!

User RedEight pointed out that I messed up the parse regex for UNTIL values
when I made the recent change regarding DATE-type UNTILs. That's fixed, now.

In addition, I tweaked the iCalcreator version detection regex to be a bit
more forgiving of any possible changes the author makes in his version
definition code.

There's a new setting on the "iCal parser" settings page, which lets you set
an integer number of days. Events which ended more than that number of days
before the import will be skipped.

This makes it consistent with the "DateField: Repeat Rule" feeds target
offered by the Date module. It also pushes the source up next to the
"Date: Start" and "Date: End" sources, which helps you find it when you're
setting up your mapping.

This is only a UI change.

According to the iCal spec, the UNTIL value of an RRULE must be specified in
UTC. But certain iCal feed creation tools don't respect this rule, and
instead specify the UNTIL value in local time. Since all the other code that
Date iCal utilizes to parse RRULEs expects the UNTIL value to be in UTC,
this go badly when it's not.

In order to get around this issue, I've added an option to the iCal Parser
settings, which allows users to tell Date iCal that they expect the UNTIL
values in their feeds' RRULEs to not be in UTC. With that option enabled,
Date iCal will treat the UNTIL date as being in the same timezone as the
event's DTSTART.

Upon further research, I discovered that my previous write-up about this
setting was incomplete and partially incorrect. I also discovered the
glaring bugs in the "Date's time zone" setting, so I added a warning against
using it.

Date iCal doesn't currently use this new mechanism (I originally created it
for a feature that ultimately didn't end up needing it), but it may be
helpful in the future for when one handler needs to know about the results
from a previous handler's pass over the same event.

All day events which start on the last day of a month and don't have an end
date specified were broken, due to a silly mistake I made in the DTEND
emulation.

This hook allows modules to alter the final data array for each event,
just before it gets sent through the rest of the Feeds processing steps to
be turned into a node. The context array is what separates this hook's
functionality from what users can do with Feeds Tamper.

Made a few other improvements to the README while I was at it.

By using the amazing, free database of Windows timezone names curtesy of the
CLDR project (http://cldr.unicode.org), I was able to add support for the
non-standard timezone names created by Microsoft Outlook. Hopefully, the
"not a valid timezone" error will now be much less common.

The Date Repeat module’s date_repeat_build_dates() function does not support
RDATEs and EXDATEs defined as separate properties, as well as being a bit
buggy in other ways. So I copy-pasta’d it and made the necessary fixes.

I wanted to add support for EXRULEs, but it’s more complicated than I
expected. So since no one has actually asked for it, I left it as a TODO.

Date iCal 3's use of the Libraries APIs was slightly less awful than 2's, but it
would still fail to properly detect an incorrectly installed iCalcreator.

This is a forward-port of the fix that I just submitted to the 2.x branch.

Because OSX uses a case-insensitive file system, git didn't pick up the change
I made when I re-wrote the parser. In retrospect, I probably should have chosen
a totally new name for the feeds parser, but the existing filename *was* the
most appropriate name for the new class, just with different capitalization.

As jakemonO pointed out, the Calendar will not display All Day events which have no
end date value, which means that Date iCal's method of leaving off the end date for
single-day All Day events was a really bad idea. Fortuantely, setting the end date
to the same day as the start date makes the date node display correctly for single-
day events, which was the reason that the end date was being left off in the first
place. This means that every All Day event can simply have it's end date rewound by
one day, and all is well in both the node display and the Calendar.

User oskar_calvo discovered that if you update Date iCal from 1.x, but
don't also install the Libraries module, you'll get a fatal error when Date iCal
attempts to check for the iCalcreator library, because the libraries_detect()
function doesn't exist.

Now, you'll instead see an error in the site requirements.

Rather than defaulting an an illegal value, the Fields plugin's settings
form now offers "First populated Date field" as the default option for
"Date field". Using this option will tell Date iCal to look through all the
fields in the View until it finds a populated Date field, and use that field.

So, if there are two Date fields specified in the view's FIELDS setting, and
at runtime the value of the first one is empty (e.g. because the node
doesn't use that field), then the second Date field's value will be used.

The update hook now also checks for importers which are set to the new parser,
but still have un-capitalized source keys. This will help users who forget to
run the database update before manually fixing the missing
DateIcalIcalcreatorParser warning.

This commit adds the migration code that converts all Feeds Importers which used
the DateIcalIcalcreatorParser plugin to use DateiCalFeedsImporter instead. The
old classes have been removed.