Make JavaScript function wrappers typesafe.

Use the v8::Signature parameter to FunctionTemplate::New to guarantee that
the info->Holder() is of the proper type when `php_v8js_php_callback` is
invoked.

Add test case demonstrating the segfault (which is now prevented).
Support g++-4.6 in configuration script.

gcc 4.6 doesn't have the -std=c++11 option, it uses the not-yet-finalized
-std=c++0x option.  Use whichever is found to be appropriate at configure
time.
Hookup Travis continous integration test server.
Merge pull request #51 from cscott/typesafe-func

Make JavaScript function wrappers typesafe.
Merge pull request #52 from cscott/travis

Support g++-4.6 and travis CI server.
Add v8 debug support
Unlock isolate on JS->PHP transition.