Adjust dependencies to fix `make stage-qa'.

Error: /usr/local/lib/libtelepathy-qt4-farstream.so.2.0.9.6.1 is linked to /usr/local/lib/libgobject-2.0.so.0 from devel/glib20 but it is not declared as a dependency
Warning: you need USE_GNOME+=glib20
Error: /usr/local/lib/libtelepathy-qt4-farstream.so.2.0.9.6.1 is linked to /usr/local/lib/libglib-2.0.so.0 from devel/glib20 but it is not declared as a dependency
Warning: you need USE_GNOME+=glib20
Error: /usr/local/lib/libtelepathy-qt4-farstream.so.2.0.9.6.1 is linked to /usr/local/lib/libintl.so.8 from devel/gettext-runtime but it is not declared as a dependency
Warning: you need USES+=gettext