Do not use g_slist_free_full() which requires glib2 2.28.0 (Frank Bergmann)
mcabber does not build on RHEL5.
The root cause is that mcabber uses g_slist_free_full which is available since
glib2 2.28.0 but configure checks only for 2.14.0.
This patch substitutes the g_slist_free_full call.
Frank Bergmann