Implement a stub Close() in File so subclasses don't have to.
Style cleanup. Also remove NaClDebug and replace with fprintf.
Add newlines to all fprintf calls.
Clean up initial screen and add lots of info to it. Bump version.
Fix bug with recvfrom() emulation; bump version.

In UDP::Receive(), if there were no packets to read, it was returning 0
instead of -1 and EWOULDBLOCK. This caused Mosh to go crazy, because there is
a circumstance where it creates a lot of sockets and tries to read from all of
them, regardless of the result of pselect(). I didn't realize Mosh would
behave like that; regardless, the emulation of recvfrom() shouldn't be wrong.
This manifested as a crypto error, went into a spin, and rendered the session
useless.

Also fixed the NativeUDP::Received() callback to bail if it gets a negative
result.