Log Message:
Completing the upgrade to Cacti v1.2.3.

Funny enough, the previous commit coincided with my own work on a
package upgrade. It brought a few bits and bobs I had been missing,
and my work closes a few of its gaps.

In detail:

INSTALL - set CACTI_USER and APACHE_GROUP properly

MESSAGES - mention newer PHPs' php.d, while updating the extension list
           mention <https://github.com/Cacti/cacti/issues/2621> setup problem

Makefile - add mandatory dependencies: php-{json,zlib,mbstring,posix}
           add patched files to 'paths' substitution

files/httpd-cacti.conf - convert to Apache 2.4 ACL syntax

patches/ - comments, CACTI_LOGDIR substitution

Minor touch-ups everywhere - I am sure there is more to do.

The result pkglints, builds, installs, configures (taking the above
#2621 into account), and runs.