Add ECDH support.

Additional changes:
 - use EC_GROUP_get_degree() in apps/req.c
 - add ECDSA and ECDH to apps/speed.c
 - adds support for EC curves over binary fields to ECDSA
 - new function EC_KEY_up_ref() in crypto/ec/ec_key.c
 - reorganize crypto/ecdsa/ecdsatest.c
 - add engine support for ECDH
 - fix a few bugs in ECDSA engine support

Submitted by: Douglas Stebila <douglas.stebila@sun.com>