changing ffmpeg to only update when required

Original commit message from CVS:
changing ffmpeg to only update when required

m4/as-slurp-ffmpeg.m4

-dnl slurp-ffmpeg.m4 0.1.0
+dnl slurp-ffmpeg.m4 0.1.1
 dnl a macro to slurp in ffmpeg's cvs source inside a project tree
 dnl taken from Autostar Sandbox, http://autostars.sourceforge.net/
 
 dnl Usage:
-dnl AS_SLURP_FFMPEG(DIRECTORY, DATE, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]])
+dnl AS_SLURP_FFMPEG(DIRECTORY, DATE, [ACTION-IF-WORKED [, ACTION-IF-NOT-WORKED]]])
 dnl
 dnl Example:
-dnl AM_PATH_FFMPEG(lib/ffmpeg, "2002-12-14 12:00 GMT")
-nl
+dnl AM_PATH_FFMPEG(lib/ffmpeg, 2002-12-14 12:00 GMT)
+dnl
+dnl make sure you have a Tag file in the dir where you check out that
+dnl is the Tag of CVS you want to have checked out
+dnl it should correspond to the DATE argument you supply, ie resolve to
+dnl the same date
+dnl (in an ideal world, cvs would understand it's own Tag file format as
+dnl a date spec)
 
 AC_DEFUN(AS_SLURP_FFMPEG,
 [
@@ -20,24 +26,30 @@ AC_DEFUN(AS_SLURP_FFMPEG,
   if test ! -d ffmpeg/CVS; then
     # check out cvs code
     AC_MSG_NOTICE(checking out ffmpeg cvs code from $2 into $1)
-    cvs -Q -d:pserver:anonymous@cvs.ffmpeg.sourceforge.net:/cvsroot/ffmpeg co -D $2 ffmpeg || FAILED=yes
+    cvs -Q -d:pserver:anonymous@cvs.ffmpeg.sourceforge.net:/cvsroot/ffmpeg co -D '$2' ffmpeg || FAILED=yes
     cd ffmpeg
   else
-    cd ffmpeg 
-    AC_MSG_NOTICE(updating ffmpeg cvs code)
-    cvs -Q update -dP -D $2 || FAILED=yes
+    # compare against Tag file and see if it needs updating
+    if diff -q Tag ffmpeg/CVS/Tag > /dev/null 2> /dev/null
+    then
+      # diff returned no problem
+      AC_MSG_NOTICE(ffmpeg cvs code in sync)
+    else
+      # diff says they differ
+      cd ffmpeg 
+      AC_MSG_NOTICE(updating ffmpeg cvs code)
+      cvs -Q update -dP -D '$2' || FAILED=yes
+    fi
   fi
   
-  # now configure it
-    AC_MSG_NOTICE(configuring ffmpeg cvs code)
-  ./configure
-
   # now go back
   cd $DIRECTORY
 
   if test "x$FAILED" == "xyes"; then
     [$4]
+    false
   else
     [$3]
+    true
   fi
 ])