Introduced the -pidfile argument with locking behaviour
Specify location of pidfile in the configuration file instead of a commandline parameter.
Add more contextual information to errors occuring while writing/reading the pidfile.
Update CHANGES.txt to reflect changes made for #777
Document pidfile configuration setting.
Code standard
Merge branch 'features/issue_777' of github.com:magnusp/heka into magnusp-features/issue_777
Update docs and changelog to reflect change in config option spelling.