* examples/rsa-keygen.c (main): Added long options. Deleted -?,

and fixed handling of bad options.

* examples/next-prime.c (main): Deleted -?, and fixed handling of
bad options.
* examples/random-prime.c (main): Likewise.

Rev: nettle/examples/random-prime.c:1.4
Rev: nettle/examples/rsa-keygen.c:1.3