blocks at a time. Handle the case of a single block specially.

Rev: nettle/ctr.c:1.3

argument.
* ctr.c: Use INCREMENT macro from macros.h, deleted local version.

Rev: nettle/ChangeLog:1.128
Rev: nettle/ctr.c:1.2
Rev: nettle/macros.h:1.3

Rev: src/nettle/ctr.c:1.1
Rev: src/nettle/ctr.h:1.1