Use unaliased grep in flag check

lib/grep.zsh

@@ -9,7 +9,7 @@ GREP_OPTIONS="--color=auto"
 VCS_FOLDERS="{.bzr,.cvs,.git,.hg,.svn}"
 
 grep-flag-available() {
-    echo | grep $1 "" >/dev/null 2>&1
+    echo | command grep $1 "" >/dev/null 2>&1
 }
 if grep-flag-available --exclude-dir=.cvs; then
     GREP_OPTIONS+=" --exclude-dir=$VCS_FOLDERS"