Manage additional packages (for modules)

[fraenki]

On some platforms (like CentOS) some modules require the installation of additional packages:

proftpd-ldap.x86_64 : Module to add LDAP support to the ProFTPD FTP server
proftpd-mysql.x86_64 : Module to add MySQL support to the ProFTPD FTP server
proftpd-postgresql.x86_64 : Module to add PostgreSQL support to the ProFTPD FTP server
proftpd-sqlite.x86_64 : Module to add SQLite support to the ProFTPD FTP server

The module should be able to automatically install all required packages, depending on the values in $load_modules.