New utility: 'pid', a thing more or less similar in concept to

Debian's pidof only souped up so as to recognise interpreted scripts
(in common languages), match command arguments, cope with shell
scripts (or indeed other programs) that have forked into pieces, try
to return a single pid for uses that won't cope with more than one,
and automatically exclude itself from its own search.

git-svn-id: svn://svn.tartarus.org/sgt/utils@9713 cda61777-01e9-0310-a592-d414129be87e