verify-commit: add option to print raw gpg status information

verify-commit by default displays human-readable output on standard
error.  However, it can also be useful to get access to the raw gpg
status information, which is machine-readable, allowing automated
implementation of signing policy.  Add a --raw option to make
verify-commit produce the gpg status information on standard error
instead of the human-readable format.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-verify-commit.txt

@@ -16,6 +16,10 @@ Validates the gpg signature created by 'git commit -S'.
 
 OPTIONS
 -------
+--raw::
+	Print the raw gpg status output to standard error instead of the normal
+	human-readable output.
+
 -v::
 --verbose::
 	Print the contents of the commit object before validating it.