prefer "hash mismatch" to "sha1 mismatch"

To future-proof ourselves against a change in the hash, let's use the
more generic "hash mismatch" to refer to integrity problems. Note that
we do advertise this exact string in git-fsck(1). However, the message
itself is marked for translation, meaning we do not expect it to be
machine-readable.

While we're touching that documentation, let's also update it for
grammar and clarity.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/sha1-file.c b/sha1-file.c
index 39cdf37..2356459 100644
--- a/sha1-file.c
+++ b/sha1-file.c
@@ -2218,7 +2218,7 @@ static int check_stream_oid(git_zstream *stream,
 
 	the_hash_algo->final_fn(real_oid.hash, &c);
 	if (!oideq(expected_oid, &real_oid)) {
-		error(_("sha1 mismatch for %s (expected %s)"), path,
+		error(_("hash mismatch for %s (expected %s)"), path,
 		      oid_to_hex(expected_oid));
 		return -1;
 	}
@@ -2270,7 +2270,7 @@ int read_loose_object(const char *path,
 		}
 		if (check_object_signature(expected_oid, *contents,
 					 *size, type_name(*type))) {
-			error(_("sha1 mismatch for %s (expected %s)"), path,
+			error(_("hash mismatch for %s (expected %s)"), path,
 			      oid_to_hex(expected_oid));
 			free(*contents);
 			goto out;