Add socketfile functionality to pfix-srsd

Add socketfile functionality to postlicyd

Add socketmap protocol support to pfix-srsd so it can be used with postfix 2.10 socketmap lookup tables which support both tcp and socketfile (tcp_table only supports tcp, and is disliked within postfix due to namespace and protocol discrepencies so we should avoid it)

Drop privileges before configuration checking in postlicyd, and print a configuration OK message if everything is good - also reuse config_reload so we properly check ALL configuration in the same way we would load it

Support the new libcommon user group daemon options

Provide xmalloc/xrealloc style functions to libsrs2 so that allocations cause abort(), libsrs2 does not appear to check malloc returns...