- output more informative error messages in `js_parse_expect`.
The previous code was bogus:
```
return js_parse_error(s, "expecting '%c'", tok);
```
this was causing a bug on `eval("do;")` where `tok` is `TOK_WHILE` (-70, 0xBA)
creating an invalid UTF-8 encoding (lone trailing byte).
This would ultimately have caused a failure in `JS_ThrowError2` if `JS_NewString`
failed when converting the error message to a string if the conversion detected the invalid
UTF-8 encoding and throwed an error (it currently does not, but should).
- test for `JS_NewString` failure in `JS_ThrowError2`
- test for `JS_FreeCString` failure in run-test262.c
- add more test cases
5a7e578482