Correctly handle (?i) in ignores (fixes #1953)

lib/fnmatch/fnmatch_test.go

@@ -53,10 +53,6 @@ var testcases = []testcase{
 	{"**/foo.txt", "bar/baz/foo.txt", PathName, true},
 
 	{"foo.txt", "foo.TXT", CaseFold, true},
-	{"(?i)foo.txt", "foo.TXT", 0, true},
-	{"(?i)(?i)foo.txt", "foo.TXT", 0, true}, // repeated prefix should be fine
-	{"(?i)**foo.txt", "/dev/tmp/foo.TXT", 0, true},
-	{"(?i)!**foo.txt", "/dev/tmp/foo.TXT", 0, false},
 
 	// These characters are literals in glob, but not in regexp.
 	{"hey$hello", "hey$hello", 0, true},