sparse-checkout: escape all glob characters on write

The sparse-checkout patterns allow special globs according to
fnmatch(3). When writing cone-mode patterns for paths containing
these characters, they must be escaped.

Use is_glob_special() to check which characters must be escaped
this way, and add a path to the tests that contains all glob
characters at once. Note that ']' is not special, since the
initial bracket '[' is escaped.

Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/sparse-checkout.c

@@ -149,7 +149,7 @@ static char *escaped_pattern(char *pattern)
 	struct strbuf final = STRBUF_INIT;
 
 	while (*p) {
-		if (*p == '*' || *p == '\\')
+		if (is_glob_special(*p))
 			strbuf_addch(&final, '\\');
 
 		strbuf_addch(&final, *p);