Don't keep the lists of source files for libglib, libgobject and
libgio in the VS project files in addition to the canonical location,
the corresponding Makefile.am files.
Instead, generate the corresponding .vcproj files at make dist time
using the C preprocessor, from template files called .vcprojin. We
still list explicitly in the .vcprojin files some of the
Windows-specific source files, and the sources files of gnulib and
pcre.
