Fixed bug #573: Service checks returns (No output on stdout) stderr

This commits adds a check to the gather_output() function in lib/worker.c.
The check verifies that the reason for a failed read is NOT that the
socket cannot be read due to a temporary unavailablility (errno == EAGAIN).
If the socket is temporarily unavailable, the function simply tries the
read again.
Merge branch 'master' of ssh://git.code.sf.net/p/nagios/nagioscore

* 'master' of ssh://git.code.sf.net/p/nagios/nagioscore:
  Main page layout changes, style and markup cleanup. Add core process status indicator.
Removed extra check for contact groups with no contacts and no contact groups