Support copy and rename detection in fast-export.

Although it does not matter for Git itself, tools that
export to systems that explicitly track copies and
renames can benefit from such information.

This patch makes fast-export output correct action
logs when -M or -C are enabled.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-fast-export.txt b/Documentation/git-fast-export.txt
index 4956964..b974e21 100644
--- a/Documentation/git-fast-export.txt
+++ b/Documentation/git-fast-export.txt
@@ -36,6 +36,15 @@
 unsigned, with 'verbatim', they will be silently exported
 and with 'warn', they will be exported, but you will see a warning.
 
+-M::
+-C::
+	Perform move and/or copy detection, as described in the
+	linkgit:git-diff[1] manual page, and use it to generate
+	rename and copy commands in the output dump.
++
+Note that earlier versions of this command did not complain and
+produced incorrect results if you gave these options.
+
 --export-marks=<file>::
 	Dumps the internal marks table to <file> when complete.
 	Marks are written one per line as `:markid SHA-1`. Only marks