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...
Documentation updates

Add myself to AUTHORS as contributor :-)
Adjust SRS documentation - it does not actualy verify the email is a bounce?
Provide sample redhat init scripts
Add original author and a teeny change log
Update readme
Update readme date
Point common to updated one
Update common submodule to latest
Fix spacing in AUTHORS

Set default postlicyd config back to port
Remove xalloc_srs and xrealloc_srs as they are now _unsigned in libcommon

Greatly simplify and reduce code for netstring_encode_and_send

Use new start_(tcp|unix)_listener naming

Drop unnecessary inline keywords

Code readability improvements and formatting adjustments
Remove xrealloc_srs and xmalloc_srs which were moved to libcommon as _unsigned

Use new start_(unix|tcp)_listener function naming

Formatting fixes
Update common
Add header_recipient to pfix-srsd postfix config example, so bounces show the original email in the To: header instead of the SRS address since only the RCPT TO was rewritten
Normalise switch/case spacing and increase readability
Fix links
Detab asciidocs to 4 spaces
Show a TCP table example first, as it is default
Update common reference
Fix netstring_encode_and_send undeclared i