Clean/fix up the Preprocessor Definitions for the various projects, where
we purge out the unneeded macros and add _DEBUG to the Debug builds of
various projects that somehow lacked this.
This will also fix the GIO build under Visual C++ 2008, as the _DEBUG macro
in the release builds will cause a debug entry to appear in its manifest
file during the build, which will cause GIO-using applications to fail
to run on systems not running Visual C++/Studio 2008 due to its embedding
of a badly-generated manifest file.
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.
