This change alters the processing of invalid, RSA pre-master secrets so
that bad encryptions are treated like random session keys in constant
time.
Don't SEGFAULT when trying to export a public DSA key as a private key.
Limit the number of empty records that will be processed consecutively
in order to prevent ssl3_get_record from never returning.

Reported by "oftc_must_be_destroyed" and George Kadianakis.