Provide a ssl3_get_cipher_by_id() function that allows ciphers to be looked
up by their ID. For one, this avoids an ugly mess in ssl_sess.c, where the
cipher value is manually written into a buffer, just so the cipher can be
located using ssl3_get_cipher_by_char().

ok bcook@ miod@
Currently, ssl3_put_char_by_bytes(NULL, NULL) is just a long handed way
of writing "2". Add a define for the SSL3_CIPHER_VALUE_SIZE (rather than
using a less-readable hardcoded constant everywhere) and replace the
ssl3_put_char_by_bytes(NULL, NULL) calls with it.

ok bcook@ miod@