perlipc: strict safety, consistency, cleanup

perlipc: strict safety, consistency, cleanup

* made all examples consistently strict-safe
* included 'use strict' and 'use warnings' in all "full" examples
* removed -w from shebangs (replaced by 'use warnings')
* removed inconsistent forward declaration of variables
* mention in IO::Handle comment that it's only needed before 5.14
* link to core modules IPC::Open2, IPC::Open3, and Socket
* add required waitpid to IPC::Open2 example
* removed unnecessary usage of English
* removed unnecessary usage of FileHandle