Detect successful exit of job using file based system instead of polling

[ssadedin]

Currently Bpipe relies on frequently polling the queue manager to know that a job exited.

This could be avoided if every job writes out an exit code / status file at successful completion. Then Bpipe can simply poll for the existence of the file rather than constantly querying the queue manager.

see #213, #35, #211.

[gdevenyi]

Could bpipe use inotify for this instead of polling? http://markusjais.com/file-system-events-with-java-7/

[ssadedin]

In fact, it does use inotify already for file based events, but unfortunately that presents its own issues - see #210.