Initialize v8js_globals manually only if ZTS is enabled.

If ZTS is disabled, the v8js_globals instance is declared right in the BSS and hence automatically initialized by C++ compiler.  Most of the variables are just zeroed, hence no need to initialized them manually any longer

If ZTS is enabled however, v8js_globals just points to a freshly allocated, unitialized piece of memory, hence we need to initialize all fields on our own.  Likewise on shutdown we have to run the destructors manually.

I suppose @cscott tested his pull request #66 with ZTS enabled an hence everything looked alright.  Could you please confirm that?

cheers
  stesie