Title: check_mk_agent.linux: fix situation where async plugin is not executed after crash
Level: 1
Component: checks
Compatible: compat
Version: 1.2.6b1
Date: 1417615386
Class: fix

When executing asynchronous sections or plugins the Check_MK Agent uses
<tt>run_cached()</tt> for putting them in the background. This function
creates a cachefile with the extension <tt>.new</tt> and removes that suffix
when the actual plugin has finished. If due to a server crash the file keeps
lying around the the plugin would not be executed anymore.

We now remove that file if it is older then twice the cache age <i>and
we kill</i> any process that still has open that file. That way we avoid
overlapping plugins in case of a real hanger.
