(Imported from upstream's e4676e900f165f5272991443225813002300b09b.)

Change-Id: I678e158c223daf2f7f9114f4e743d531fe2e2a93
Reviewed-on: https://boringssl-review.googlesource.com/4044
Reviewed-by: Adam Langley <agl@google.com>

Everything before crypto/ec.

Change-Id: Icbfab8e4ffe5cc56bf465eb57d3fdad3959a085c
Reviewed-on: https://boringssl-review.googlesource.com/3401
Reviewed-by: Adam Langley <agl@google.com>

Change-Id: I2bf0144aaa8b670ff00b8e8dfe36bd4d237b9a8a
Reviewed-on: https://boringssl-review.googlesource.com/3140
Reviewed-by: Adam Langley <agl@google.com>

Ensure that, when generating small primes, the result is actually of the
requested size. Fixes OpenSSL #2701.

This change does not address the cases of generating safe primes, or
where the |add| parameter is non-NULL.

Initial fork from f2d678e6e8 (1.0.2 beta).

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