Use "-M" instead of "-C" for "git diff" and "git status"

The "C" in "-C" may stand for "Cool", but it's also pretty slow, since
right now it leaves all unmodified files to be tested even if there are
no new files at all.  That just ends up being unacceptably slow for big
projects, especially if it's not all in the cache.

git-diff-script

@@ -3,13 +3,13 @@ rev=($(git-rev-parse --revs-only "$@"))
 flags=($(git-rev-parse --no-revs "$@"))
 case "${#rev[*]}" in
 0)
-	git-diff-files -p "$@";;
+	git-diff-files -M -p "$@";;
 1)
-	git-diff-cache -p "$@";;
+	git-diff-cache -M -p "$@";;
 2)
 	begin=$(echo "${rev[1]}" | tr -d '^')
 	end="${rev[0]}"
-	git-diff-tree -p $flags $begin $end;;
+	git-diff-tree -M -p $flags $begin $end;;
 *)
 	echo "I don't understand"
 	exit 1;;

git-status-script

@@ -27,7 +27,7 @@ report () {
 }
 
 git-update-cache --refresh >& /dev/null
-git-diff-cache -B -C --cached HEAD | sed 's/^://' | report "Updated but not checked in" "will commit"
+git-diff-cache -M --cached HEAD | sed 's/^://' | report "Updated but not checked in" "will commit"
 committable="$?"
 git-diff-files | sed 's/^://' | report "Changed but not updated" "use git-update-cache to mark for commit"
 if [ "$committable" == "0" ]