Make EVP_Digest* work again.
Fix copy for CCM, GCM and XTS.

Internal pointers in CCM, GCM and XTS contexts should either be
NULL or set to point to the appropriate key schedule. This needs
to be adjusted when copying contexts.
(cherry picked from commit c2fd5d79ffc4fc9d120a0faad579ce96473e6a2f)
Merge remote-tracking branch 'upstream/OpenSSL_1_0_2-stable' into 1.0.2-chacha