configure.ac: uncomment gettext version setup
configure.ac: uncomment gettext version setup

Fixes autogen.sh. It would run autopoint, which would complain
that it could not find the gettext version in configure.ac.

https://bugzilla.gnome.org/show_bug.cgi?id=748058

barisdemiray/gst-rtsp-server,thaytan/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server,surround-io/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server