Make all tests pass under ::PP

This changes tests so that they run under ::PP as well as the XS version.

It then fixes some errors so that they're the same as the XS version, adds some API compatibility and makes Ipv6 work.

There are two outstanding issues

* A spurious  ```Subroutine IO::Socket::INET6::sockaddr_in6 redefined``` warning 
* I cannot for the life of me make DGRAM tests work under PurePerl - they fail with ```Error in ->set_receiver: Protocol wrong type for socket at lib/Log/Syslog/Fast/PP.pm line 143```