Test driver for Diffie-Hellman key agreement operations.

This program generates Diffie-Hellman moduli and does a sample
key agreement with them.

The command line is a seed string which is used to generate the
public modulus.  The use of a seed lets you verify that the
modulus was not generated in a weak manner.

Currently, the list of key sizes to generate is compiled in.

After key generation, the program performs a sample key agreement.

The primes used in SKIP were generated with the seed in the file
Gandhi, which contains 79 bytes plus a newline:
Whatever you do will be insignificant, but it is very important that you do it.

Example invocation lines:

dhtest arbitrary seed string
dhtest `cat Gandhi`
