read_gitfile_gently(): rename misnamed function to read_gitfile()

The function was not gentle at all to the callers and died without giving
them a chance to deal with possible errors. Rename it to read_gitfile(),
and update all the callers.

As no existing caller needs a true "gently" variant, we do not bother
adding one at this point.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

@@ -139,7 +139,7 @@ char *git_path_submodule(const char *path, const char *fmt, ...)
 		strbuf_addch(&buf, '/');
 	strbuf_addstr(&buf, ".git");
 
-	git_dir = read_gitfile_gently(buf.buf);
+	git_dir = read_gitfile(buf.buf);
 	if (git_dir) {
 		strbuf_reset(&buf);
 		strbuf_addstr(&buf, git_dir);