Quote sigs for status.pid selectively

Will quote if the sig doesn't end with ' or ", and if it doesn't begin
with -.  This is to prevent it from quoting sigs like:

'someregex'
-E someregex
-E 'someregex'  <-- Why we check for trailing quotes, not leading
Add documentation to tell why we chose to quote as we did
Merge pull request #3906 from basepi/pidsigfix3728

Fixes #3728 Selectively quote sigs for status.pid