EC_POINT is split into the existing public EC_POINT (where the caller is
sanity-checked about group mismatches) and the low-level EC_RAW_POINT
(which, like EC_FELEM and EC_SCALAR, assume that is your problem and is
a plain old struct). Having both EC_POINT and EC_RAW_POINT is a little
silly, but we're going to want different type signatures for functions
which return void anyway (my plan is to lift a non-BIGNUM
get_affine_coordinates up through the ECDSA and ECDH code), so I think
it's fine.

This wasn't strictly necessary, but wnaf.c is a lot tidier now. Perf is
a wash; once we get up to this layer, it's only 8 entries in the table
so not particularly interesting.

Bug: 239
Change-Id: I8ace749393d359f42649a5bb0734597bb7c07a2e
Reviewed-on: https://boringssl-review.googlesource.com/27706
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>