Stop creating RSA objects we don't use in RSA key exchange. Some code style changes.
Fixed time invariance issues when decoding the premaster secret.
Debug cleanup.
SSL.File: Improved backend robustness.

Don't bother running the backend if the peer has aborted the connection.
SSL.File: Fail write() on ALERT.

write() now fails with EIO if the peer has aborted the connection
with a fatal alert.