Fix building introspection when srcdir != builddir
Fix building introspection when srcdir != builddir

The Makefile.am snippets were making the assumption that all
the files were in the srcdir, which isn't true for generated files
with srcdir != builddir

https://bugzilla.gnome.org/show_bug.cgi?id=617892

pwithnall/totem-pl-parser,pwithnall/totem-pl-parser,MathieuDuponchelle/totem-pl-parser,MathieuDuponchelle/totem-pl-parser,MathieuDuponchelle/totem-pl-parser,MathieuDuponchelle/totem-pl-parser