Fix configure regexp for enabling FFmpeg features

All features were disabled because of a regexp that used "[^ ]" to
match start of a word. '^' is not a metacharacter meaning beginning
of line inside [], instead it inverts the matching condition of the
other characters in the list.

Changed to use "\<" and "\>" for start/end of word instead. I don't know
how standard those are, at least they're better than the previous
version.


git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@23862 b3059339-0415-0410-9bf9-f77b7e298cf2

configure

@@ -7518,7 +7518,7 @@ ff_config_enable () {
 _nprefix=$3;
 test -z "$_nprefix" && _nprefix='CONFIG'
 for part in $1; do
-  if ` echo $2 | grep "[^ ]$part[ $]" > /dev/null `; then
+  if ` echo $2 | grep "\<$part\>" > /dev/null `; then
     echo "#define ${_nprefix}_$part 1"
     echo "#define ENABLE_$part 1"
   else