Use uniform description for the '--' option.

All descriptions of the '--' option were the same except for that in
Documentation/git-merge-index.txt.

Signed-off-by: Nikolai Weibull <nikolai@bitwi.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/Documentation/git-merge-index.txt b/Documentation/git-merge-index.txt
index 6030642..fbc986a 100644
--- a/Documentation/git-merge-index.txt
+++ b/Documentation/git-merge-index.txt
@@ -20,7 +20,7 @@
 OPTIONS
 -------
 --::
-	Interpret all following arguments as filenames.
+	Do not interpret any more arguments as options.
 
 -a::
 	Run merge against all files in the index that need merging.