add fork to HAVE_LIST

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@9563 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -666,6 +666,7 @@ HAVE_LIST="
     fast_64bit
     fast_cmov
     fast_unaligned
+    fork
     freetype2
     imlib2
     inet_aton