config.c: Escape backslashes in section names properly

If an element of the configuration key name other than the first or last
contains a backslash, it is not escaped on output, but is treated as an
escape sequence on input. Thus, the backslash is lost when re-loading
the configuration.

This patch corrects this by having backslashes escaped properly, and
introduces a new test for this bug.

Signed-off-by: Bryan Donlan <bdonlan@fushizen.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.c

@@ -680,7 +680,7 @@ static int store_write_section(int fd, const char* key)
 	if (dot) {
 		strbuf_addf(&sb, "[%.*s \"", (int)(dot - key), key);
 		for (i = dot - key + 1; i < store.baselen; i++) {
-			if (key[i] == '"')
+			if (key[i] == '"' || key[i] == '\\')
 				strbuf_addch(&sb, '\\');
 			strbuf_addch(&sb, key[i]);
 		}

t/t1303-wacky-config.sh

@@ -34,4 +34,10 @@ test_expect_success 'add key in different section' '
 	check section2.key bar
 '
 
+SECTION="test.q\"s\\sq'sp e.key"
+test_expect_success 'make sure git-config escapes section names properly' '
+	git config "$SECTION" bar &&
+	check "$SECTION" bar
+'
+
 test_done