Sys::Syslog patch to allow unix domain sockets

Sys::Syslog patch to allow unix domain sockets

Thank you to Tim Bunce and Tom Phoenix for insights on making the
patched code faster and safer, and pointing out bugs.

  What follows is a "fresh patch over the 5.004_01 version".  So reverse
the previous patch before adding this one just to be safe.

 CHANGES (all recommended by Tim or Tom):

 - fixed bug where wrong variable was undef()ined causing attempts to
change back to INET socket to never occur
 - setlogsock() now croaks on any value other than 'unix' or 'inet'
 - setlogsock() no longer uses pattern matching, but is still
case-insensitive
 - updated documentation

p5p-msgid: 33B31342.7EB16A44@sc.maricopa.edu