Check for snapshot_version in source dir.

Originally committed as revision 21065 to svn://svn.ffmpeg.org/ffmpeg/trunk

version.sh

 #!/bin/sh
 
 # check for SVN revision number
-revision=$(cat snapshot_version 2> /dev/null)
+revision=$(cd "$1" && cat snapshot_version 2> /dev/null)
 test $revision || revision=$(cd "$1" && LC_ALL=C svn info 2> /dev/null | grep Revision | cut -d' ' -f2)
 test $revision || revision=$(cd "$1" && grep revision .svn/entries 2>/dev/null | cut -d '"' -f2)
 test $revision || revision=$(cd "$1" && sed -n -e '/^dir$/{n