simple,configurable check to exit on failed tcp writes

Currently, heked configured to write to a remote TCP socket will not recover from that remote TCP socket changing state ie. going through a restart or simply closing down.

I propose the option to configure hekad exit on failed writes to that remote socket.

I spent a few hours dreaming up re-connects, but was never satisfied with any solution when really I desire that any local plugins or downstream agents be made aware of a failed write (in my case a logfile reader which can benefit from not advancing the index thereby utilizing a disk buffer of sorts.)

This solution implies moving any desired restart behavior into a process manager like circus, upstart, etc.. It's easy to comprehend and configure and should be backwards compatible with existing config files.