Generate .pc files for the package, so that it would be easier for
building introspection for packages that depend on GTK+. Also split
PythonPath into PythonPath and PythonPathX64 to facilitate the build of
introspection files, which need to have Python that is built with the
same ac=rchitecture where GTK+ is built.
Clean up the formatting and spacing a bit.
Build the gtk-update-icon-cache, gtk-builder-tool and gtk-query-settings
tools and run gtk-update-icon-cache as part of the post-build
"installation" process.
Pointed out (and reminded) by Paolo Borelli in bug 759436 that we should
build, "install" and run gtk-update-icon-cache in the MSVC builds as well.
"Add" Visual Studio 2015 projects by what we did before: Copy the Visual
Studio 2010 project files and replace the items in there as needed, as
the formats of the 2010 and 2015 projects are largely the same.
