This gives us systematic bounds-checking on all the parses. Also adds a
convenience function, CBS_memdup, for saving the current contents of a CBS.
Change-Id: I17dad74575f03121aee3f771037b8806ff99d0c3
Reviewed-on: https://boringssl-review.googlesource.com/1031
Reviewed-by: Adam Langley <agl@google.com>
Initial fork from f2d678e6e89b6508147086610e985d4e8416e867 (1.0.2 beta).
(This change contains substantial changes from the original and
effectively starts a new history.)