Automate finding local-copy of libsvm for testing
https://git.uwaterloo.ca/nguenthe/statasvm/blob/master/COMPILE.md#windows-1 has an out of date set of instructions for pointing a Windows at the installed copy of libsvm; this is unnecessary on the *nixes because their package managers and default path set ups point things at the correct places, but Windows doesn't benefit from this. For this reason, we include libsvm at /src/windows/; the Windows_NT.mk file could set the LIB, PATH and INCLUDE variables, instead of requiring us to do it by hand.