Make postfix-pgsql multi-version #338

[root@mail-new ~]# pkgin show-deps postfix-pgsql
direct dependencies for postfix-pgsql-3.6.4
        postgresql13-client>=13.1nb1
        postfix-3.6.4{,nb[0-9]*}
        gcc10-libs>=10.3.0
        db4>=4.8.30

[root@mail-new ~]# pkgin in postfix postfix-pgsql
calculating dependencies...done.

2 packages to install:
  postfix-pgsql-3.6.4 postgresql13-client-13.7

0 to refresh, 0 to upgrade, 2 to install
17K to download, 17M to install

proceed ? [Y/n]
postfix-pgsql-3.6.4.tgz                                                                                                                                                 100%   17KB  17.3KB/s   00:00
installing postfix-pgsql-3.6.4...
installing postgresql13-client-13.7...
pkg_install warnings: 0, errors: 3
pkg_install error log can be found in /var/db/pkgin/pkg_install-err.log

[root@mail-new ~]# tail /var/db/pkgin/pkg_install-err.log
pkg_add: 1 package addition failed
---Jul 06 16:20:39: installing dovecot-pigeonhole-0.5.19...
---Jul 06 16:26:23: installing postfix-pgsql-3.6.4...
pkg_add: Conflicting PLIST with postgresql14-client-14.4: bin/clusterdb
pkg_add: Can't install dependency postgresql13-client>=13.1nb1
pkg_add: Expected dependency postgresql13-client>=13.1nb1 still missing
pkg_add: 1 package addition failed
---Jul 06 16:26:24: installing postgresql13-client-13.7...
pkg_add: Conflicting PLIST with postgresql14-client-14.4: bin/clusterdb
pkg_add: 1 package addition failed