Experimental handling of import libs on windows.
no longer tread linker warnings as errors.

we're missing pdb files for most of the new third-party libraries (osl, oiio, etc.) and this causes warnings in debug.
Merge branch 'est_win_import_libs' of https://github.com/est77/appleseed

Conflicts:
	src/cmake/config/win-vs100.txt
	src/cmake/config/win-vs110.txt
cosmetics.