Standards.BSON: some more tests
Standards.BSON: check for stack overflow
Standards.BSON: keep intermediate values on the stack

By keeping intermediate values on the pike stack, they are freed
automatically when a parsing error occurs.
Standards.BSON: use TYPEOF for compat with ATOMIC_SVALUE
SSL.Cipher: Use a larger group for Diffie-Hellman.

Added MODP groups 5, 14, 15, 16, 17 and 18 from RFC 3526.

Added MODP groups 22, 23 and 24 from RFC 5114.

Now defaults to using MODP group 24 (ie a 2048-bit group with
a 256-bit prime order subgroup).
Compiler: Fixed variant zapping of reference #0.

The variant dispatcher collector was missing an offset, and always
zapped the modifier bits for identifier reference #0. This has the
effect that identifier reference #0 got the modifier bits intended
for the last variant dispatcher in the class.
Crypto.DH: Added module.

This module currently just contains the DHParameters class and
the MODP groups from RFC 2409, RFC 3526 and RFC 5114. Actual
Diffie-Hellman key-exchange is not implemented here (yet).
Crypto.DH: Removed some debug.
Compiler: Fixed type derivation for attributed getters.

The getter/setter variable should now get the correct type even
when the getter/setter functions have been marked as deprecated.
Build: Get rid of some C++-style comments.