status: support --porcelain[=<version>]

Update --porcelain argument to take optional version parameter
to allow multiple porcelain formats to be supported in the future.

The token "v1" is the default value and indicates the traditional
porcelain format.  (The token "1" is an alias for that.)

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-status.txt b/Documentation/git-status.txt
index e1e8f57..6b1454b 100644
--- a/Documentation/git-status.txt
+++ b/Documentation/git-status.txt
@@ -32,11 +32,14 @@
 --branch::
 	Show the branch and tracking info even in short-format.
 
---porcelain::
+--porcelain[=<version>]::
 	Give the output in an easy-to-parse format for scripts.
 	This is similar to the short output, but will remain stable
 	across Git versions and regardless of user configuration. See
 	below for details.
++
+The version parameter is used to specify the format version.
+This is optional and defaults to the original version 'v1' format.
 
 --long::
 	Give the output in the long-format. This is the default.
@@ -96,7 +99,7 @@
 
 -z::
 	Terminate entries with NUL, instead of LF.  This implies
-	the `--porcelain` output format if no other format is given.
+	the `--porcelain=v1` output format if no other format is given.
 
 --column[=<options>]::
 --no-column::