improved error output, start on Error.captureStackTrace and usage of Error.prepareStackTrace
add JavaScriptStackTraceApi tests
respect Error.stackTraceLimit, pass JS Array of CallSite objects to Error.prepareStackTrace, improve CallSite object itself
clean up error_constructor a bit, hide _frames in metatable instead
fix bug where first frame got dropped/ignored as `this` paramter when making JS Array, and off-by-one error introduced trying to compensate
implement the trivial CallSite getters
check .name instead of .type in tests, now they pass under v8 too
Error properties vs. prototype fixup/simplification, and fixes #457
remove redudant log line, e.stack normally includes the error+message already
fix pythonbrain typo that broke [object Error] string
handle case where custom subclass does not trigger captureStackTrace
Merge #455 r=@johnnyman727: Support for JavaScript StackTrace API

Fixes #256.

Still needs:
- [x] tests
- [x] respect `Error.stackTraceLimit`
- [x] provide proper `CallSite` objects to `Error.prepareStackTrace`