Change incorrect "remote branch" to "remote tracking branch" in C code

(Just like we did for documentation already)

In the process, we change "non-remote branch" to "branch outside the
refs/remotes/ hierarchy" to avoid the ugly "non-remote-tracking branch".
The new formulation actually corresponds to how the code detects this
case (i.e. prefixcmp(refname, "refs/remotes")).

Also, we use 'remote-tracking branch' in generated merge messages (by
merge an fmt-merge-msg).

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge.c

@@ -403,7 +403,7 @@ static void merge_name(const char *remote, struct strbuf *msg)
 			goto cleanup;
 		}
 		if (!prefixcmp(found_ref, "refs/remotes/")) {
-			strbuf_addf(msg, "%s\t\tremote branch '%s' of .\n",
+			strbuf_addf(msg, "%s\t\tremote-tracking branch '%s' of .\n",
 				    sha1_to_hex(branch_head), remote);
 			goto cleanup;
 		}