Rename ssl3_record_sequence_update() to ssl3_record_sequence_increment(),
so that it reflects what it is actually doing. Use this function in a
number of places that still have the hand rolled version.

ok beck@ miod@
The OPENSSL_cleanse() in aes_gcm_cleanup() only cleans the gcm field of the
EVP_AES_GCM_CTX, leaving the AES key untouched - clean the entire context,
rather than just part of it.

ok beck@ miod@
Add missing OPENSSL_cleanse() in aead_aes_gcm_cleanup().

ok beck@ miod@
Simplify EVP_CIPHER_CTX_new() - stop pretending that EVP_CIPHER_CTX_init()
does something special... just use calloc() instead.

ok beck@ miod@
Simplify EVP_MD_CTX_create() by just using calloc(). Also, use 0 rather
than '\0' for several memset().

ok beck@ miod@