Correctly load utf8 data; add a test test-fs-read-file-sync.js

This makes it so that inspecting objects from other contexts works as expected.

Don't treat sys.inspect special, same with prototype objects.

Allow throttling from outgoing messages.

Improve test-fs-read-stream test.

Patch submitted to V8: http://codereview.chromium.org/2282003/show

Notes:
- Currently only accepts numeric user and group ids.
- No tests, as tests depend on getpwuid and getgrgid.
- No documentation, as there is no tests and this is experimental.

Test from Mark Hansen (mark at markhansen.co.nz)

And do proper utf8 encoding.

Make path.extname return an empty string also if:
- The last dot is not in the last path component
- The last dot starts the last path component