"Install" the .pdb files that were generated along with the build, to make
it easier for people to develop and debug GTK+, especially when used as a
stack, and as the .pdb files are already generated with all builds.

Also make the copy of the .dll, .lib and .exe files more selective so that
we do not accidently copy files that are not meant to be "installed", or
end up making extra copies of plugin DLLs in the wrong places, when the
projects here are included as a part of a grand solution that is used to
build the entire GTK+ stack, for example.