Update autotools configuration a bit

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=616803
add missing gobject-introspection annotations

(cherry picked from commit f3175ae198816e5c5a80b9e8a1288dbf1de2f28c)
Signed-off-by: Emmanuele Bassi <ebassi@gnome.org>
add gobject-introspection support

(cherry picked from commit 8ba11ba74fbdf00fc2a719db175e054f4c96354c)

Signed-off-by: Emmanuele Bassi <ebassi@gnome.org>
Remove copy of introspection.m4

Rely on gobject-introspection as a configure-time dependency, like most
of the GNOME platform.