Replace octal literal by unicode escape sequence

Octal literals are not allowed in strict mode.
Do not use __proto__ in util.js
Don't use `instanceof` in util.js "is" checks

While using `instanceof`, these functions could easily be faked with something
like:  Object.create(Date.prototype)
Merge pull request #11 from danyaPostfactum/strictfix

Strict mode support, drop `__proto__` usage