replace bashism with POSIX construct

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@7317 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -2066,7 +2066,7 @@ EOF
 
 pkgconfig_generate_uninstalled(){
 name=$1
-shortname=${name/lib/}
+shortname=${name#lib}
 comment=$2
 version=$3
 libs=$4