Unescaped strings in generated code in some cases

[zeen]

@:keep private function test(s: StringBuf) {
    s.addChar("\"".code);
    s.addChar("\\".code);
    s.addChar("\n".code);
}

produces

- (void) test:(StringBuf*)s{

    s.b = [NSString stringWithFormat:@"%@%@", s.b, @"""];
    s.b = [NSString stringWithFormat:@"%@%@", s.b, @"\"];
    s.b = [NSString stringWithFormat:@"%@%@", s.b, @"
"];
}

Note how the strings in the generated code are not escaped, which breaks the code.