Make the projects include a single property sheet as necessary, which will
in turn include the other property sheet(s) as needed, so that we can avoid
warnings where we include the same property sheets twice in a single
project.
Also make the copying of pre-configured headers into custom build rules so
that they can be removed upon the clean command from the IDE and that they
can be re-copied if their counterpart *.h.win32 are updated.
