Produce correct version string even when not run in a Subversion working copy.

based on a patch by Ismail Dönmez ismail##@##pardus##.##org##.##tr

Originally committed as revision 5511 to svn://svn.ffmpeg.org/ffmpeg/trunk

version.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
-svn_revision=`svn info | grep Revision | cut -d' ' -f2 || echo UNKNOWN`
+svn_revision=`svn info 2> /dev/null | grep Revision | cut -d' ' -f2`
+test $svn_revision || svn_revision=UNKNOWN
+
 NEW_REVISION="#define FFMPEG_VERSION \"SVN-r$svn_revision\""
 OLD_REVISION=`cat version.h 2> /dev/null`