Major fixes and cleanups

- Fix agents starter
- Get rid of passenger_tmpdir
- Replace ServerInstanceDir with InstanceDirectory
Remove support for Rails 1.2-2.2
Add admin server for the HTTP server
Fix some compilation problems on Linux
Remove trailing whitespace in some files
Fix some unit test issues

For example with libeio shutdown.
Make Nginx module work again
Fixed some bugs, added support for dechunking responses

- There was a bug in mbuf handling.
- There was a bug in handling chunked request and response bodies.
- We now dechunk all responses sent to Nginx because otherwise
  Nginx would double-chunk responses.