pp_concat: Only call SvPV_force_nolen when needed

If we just did an sv_setpvs on it, the SvPV_force_nolen should not do
anything useful, so let's not.

Side note: s/TARG/left/ in the enclosing block because they are the same
pointer, so why use a define that needs grokking by the reader of the
code if the local variable is guaranteed to be the same?
Add IO-Socket-IP to Maintainers.pl
Update IO-Socket-IP to CPAN version 0.28

  [DELTA]

0.28    2014/02/10 16:17:59
        [CHANGES]
         * Renamed internal _configure method to _io_socket_ip__configure to
           avoid clashes with modules that try to subclass IO::Socket::INET

        [BUGFIXES]
         * Disable AI_ADDRCONFIG during one-sided 'v6 tests as sometimes it
           would otherwise fail
         * Skip the SO_BROADCAST test on OSes that fail with EACCES (RT92502)
Add some examples to cv_set_call_checker and wrap_op_checker
provide a more limited change-count for acknowledgements.pl
tweak Porting/acknowledgements.pl to avoid awk and grep

Rather than assuming that we are on a unix system with the
standard kit, we can rely on this neat little programming
language that provides their behavior and is already assumed
to be present!
acknowledgements: use $^X when running sub-perl