Fix usage string of git-diff-cache and add documentation of -m flag.

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/core-git.txt

@@ -241,7 +241,7 @@ Converts old-style GIT repository to the latest.
 
 ################################################################
 git-diff-cache
-	git-diff-cache [-p] [-r] [-z] [--cached] <tree-ish>
+	git-diff-cache [-p] [-r] [-z] [-m] [--cached] <tree-ish>
 
 Compares the content and mode of the blobs found via a tree object
 with the content of the current cache and, optionally ignoring the
@@ -264,6 +264,13 @@ stat state of the file on disk.
 --cached
 	do not consider the on-disk file at all
 
+-m
+
+	By default, files recorded in the index but not checked
+	out are reported as deleted.  This flag makes
+	git-diff-cache say that all non-checked-out files are up
+	to date.
+
 Output format:
 
 See "Output format from git-diff-cache, git-diff-tree and git-diff-files"

diff-cache.c

@@ -165,7 +165,7 @@ static void mark_merge_entries(void)
 }
 
 static char *diff_cache_usage =
-"diff-cache [-r] [-z] [-p] [-i] [--cached] <tree sha1>";
+"git-diff-cache [-p] [-r] [-z] [-m] [--cached] <tree sha1>";
 
 int main(int argc, char **argv)
 {