Christopher Subich authored Nov 01, 2017 and Christopher Subich committed Nov 01, 2017

The template form of add_diagnostic<x> is attractive, but to
be properly used the template implementation must be visible
at the same time as the header file itself.  The
instantiations formerly in BaseCase.cpp were not likely to
be visible to a program, increasing compile time (if they
were re-instantiated) or causing an error (if the
implementation was not visible).  This change:

*) Moves the implementation of add_diagnostic to a new
BaseCase_impl.cc
*) Includes this impementation file from BaseCase.hpp, with
a double-inclusion guard
*) Preserves instantiations of <double> and <int>, with new
'extern' declarations in BaseCase.hpp to prevent
double-definition.