Bignum: Fixed the overflow checks for size_t.

The type UINT32 doesn't exist in Pike...

Fixes compilation issues on Solaris.
Bignum: Fixed typo.
Nettle: Fixed multiple instances of unaligned stack.

The precompile.pike RETURN (and RETURN_REF) statement(s) requires the
stack to be at the same level as at function entry. Remove the use of
RETURN from places where the stack level has changed.

Fixes the return values from set_encrypt_key() and others in multiple
wrapper classes (eg CBC, Proxy, etc).
SSL: Add support for the max_fragment_length extension.
SSL: Added some more cipher suite constants.

These suites from draft-ietf-tls-56-bit-ciphersuites-01.txt
are apparently in use by some versions of MSIE.
SSL.Constants: Added some more RFC notes.
SSL.Constants: Added TLS_dhe_dss_with_rc4_128_sha.

This suite was part of draft-ietf-tls-56-bit-ciphersuites-01.txt
and caused the testsuite to fail by not being implemented. It
also seems to be in use by gnutls 3.2.12.
SSL.context: Changed API for get_suites().

API changes as per discussion with Martin Nilsson.

get_suites() should now be more easy to use for eg client setup, and
have reasonable defaults for secure operation.

The {rsa,dsa,ecdsa}_mode() functions are now marked as deprecated,
are identical, and ignore the max_version argument.