Fix overly lenient comparisons:

    - EC_GROUP_cmp shouldn't consider curves equal just because
      the curve name is the same. (They really *should* be the same
      in this case, but there's an EC_GROUP_set_curve_name API,
      which could be misused.)

    - EC_POINT_cmp shouldn't return 0 for ERR_R_SHOULD_NOT_HAVE_BEEN_CALLED
      or EC_R_INCOMPATIBLE_OBJECTS errors because in a cmp API, 0 indicates
      equality (not an error).

    Reported by: king cope

(cherry picked from commit 312a46791ab465cfa3bf26764361faed0e5df014)