merge/pull Check for untrusted good GPG signatures

When --verify-signatures is specified, abort the merge in case a good
GPG signature from an untrusted key is encountered.

Signed-off-by: Sebastian Götte <jaseg@physik-pool.tu-berlin.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/commit.h b/commit.h
index c24b844..87b4b6c 100644
--- a/commit.h
+++ b/commit.h
@@ -234,11 +234,11 @@
 			      const char *format_last);
 
 /*
- * Check the signature of the given commit. The result of the check is stored in
- * sig->result, 'G' for a good signature, 'B' for a bad signature and 'N'
- * for no signature at all.
- * This may allocate memory for sig->gpg_output, sig->gpg_status, sig->signer
- * and sig->key.
+ * Check the signature of the given commit. The result of the check is stored
+ * in sig->check_result, 'G' for a good signature, 'U' for a good signature
+ * from an untrusted signer, 'B' for a bad signature and 'N' for no signature
+ * at all.  This may allocate memory for sig->gpg_output, sig->gpg_status,
+ * sig->signer and sig->key.
  */
 extern void check_commit_signature(const struct commit* commit, struct signature_check *sigc);