solve : crash for z^13-1

[raph-of-burgondy]

hi,

solve crashes for z^13-1 i.e. nerdamer("solve(z^13-1,z)") after a very long time (infinite loop ?)
crashes (in fact, no solution after 10 sec) also for : 12,19,20,21 - (22 is ok, not tested after)

[jiggzson]

@raph-of-burgondy, I'll take a look at all equations of this form while I'm at it.