Add option to enable deprecated
Enable deprecated in DISTCHECK_CONFIGURE_FLAGS

The problem is that without the Gstatic*Mutex the gstreamer mixer fails to build
This is because Gstatic*Mutex is deprecated in glib but still in use by gstreamer 0.10.

To have make distcheck work we enable it here.
Merge pull request #35 from infirit/master

Add --enable-deprecated and put it in DISTCHECK_CONFIGURE_FLAGS