change kex-gex server code to generate primes by hand
added a util function "generate_prime" to compare to the incredibly slow C
version, but it's no faster of course. i think kex-gex from the server is
just not going to be feasible without having a separate thread generate some
primes in the background to have handy when a request comes in. so in short,
this still doesn't work.
also i put bit_length into util and a tb_strings function which gets stack
traceback info and splits it into a list of strings.
Robey Pointer