Update to rcs version 5.9.2.
Nominally this should bring portability improvements except that it
introduces two problems on FreeBSD which we now have to patch locally:
. FreeBSD date does not feature the -r option GNU date does.
. makeinfo on FreeBSD before 10.x does not support @geq.
In addition the default for RCS_MEM_LIMIT has grown from 256kiB to
PR: 182809 (requested an update to 5.9.1)
Approved by: maintainer timeout (zeising, 5 months)