This changes EVP's cipher and digest code to hook via the ENGINE support.

This changes EVP's cipher and digest code to hook via the ENGINE support.
See crypto/engine/README for details.

- it also removes openbsd_hw.c from the build (that functionality is
  going to be available in the openbsd ENGINE in a upcoming commit)

- evp_test has had the extra initialisation added so it will use (if
  possible) any ENGINEs supporting the algorithms required.