Use >= instead of == in package depenencies
Change from Maybe import to Data.Maybe
Fix bug where start value was a random number < num bits instead of < 2^(num bits)
This commit adds parallelism to the prime search in GeneratePrime.hs.
A separate search is dispatched for each thread and there is no thread
communication.

The usage, e.g. to generate a 2048 bit prime on 4 CPU cores.

    ~$ ./GeneratePrime pprime 2048 4 +RTS -N4

I haven't performed a statistical analysis but obviously it will
not be four times as fast with four CPU cores. But the variance
will decrease and you'll be lucky more often :)