ECC code.

Change-Id: I1a960620edbb30e10dcbab0e8053a1deb9db3262
Reviewed-on: https://boringssl-review.googlesource.com/3402
Reviewed-by: Adam Langley <agl@google.com>

Including string.h in base.h causes any file that includes a BoringSSL
header to include string.h. Generally this wouldn't be a problem,
although string.h might slow down the compile if it wasn't otherwise
needed. However, it also causes problems for ipsec-tools in Android
because OpenSSL didn't have this behaviour.

This change removes string.h from base.h and, instead, adds it to each
.c file that requires it.

Change-Id: I5968e50b0e230fd3adf9b72dd2836e6f52d6fb37
Reviewed-on: https://boringssl-review.googlesource.com/3200
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

(Imported from upstream's 267e6f3cc0)

Change-Id: I99cfd0196b9625449c50494562c44f57f09fed17
Reviewed-on: https://boringssl-review.googlesource.com/2167
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

Replace the tree-like structure by a linear approach, with fewer special
cases to handle value 0.

(Imported from upstream's d5213519c0ed87c71136084e7e843a4125ecc024.)

Change-Id: Icdd4815066bdbab0d2c0020db6a8cacc49b3d82a
Reviewed-on: https://boringssl-review.googlesource.com/1400
Reviewed-by: Adam Langley <agl@google.com>

Fix handling of points at infinity in ec_GFp_simple_points_make_affine.
When inverting an array of Z coordinates, the algorithm is supposed to
treat any 0 essentially like a 1 to remain in the multiplicative group;
however, for one of the cases, we incorrectly multiplied by 0 and thus
ended up with garbage.

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)