* examples/rsa-keygen.c (main): Use xalloc for allocation.

* examples/rsa-encrypt.c (write_bignum): Likewise.
* examples/rsa-decrypt.c (read_bignum): Likewise.

Rev: src/nettle/examples/rsa-decrypt.c:1.4
Rev: src/nettle/examples/rsa-encrypt.c:1.5
Rev: src/nettle/examples/rsa-keygen.c:1.12