* Removed ToJSVal<jsval> because it's treated as ToJSVal<long> and
causes minor confusion and/or compiler errors.
Changed script interface functions to return either C++ types or a
jsval_t wrapper.
* Replaced some C casts with static_cast to avoid significant confusion
and to cause compiler errors instead.
* Removed some redundant argument-checking code. Simplified some
string-generating code.
* Fixed some "dereferencing type-punned pointer will break
strict-aliasing rules" warnings (from `g++ -O3`).
This was SVN commit r5115.
