Coord: Minor fix for 2306.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2310 ba6dc0ae-232f-0410-883f-9ebac64fc565
Coord: Replace timerfd with simpler timeout based on clock.

timerfd is a newer feature that is not available on older Kernels.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2311 ba6dc0ae-232f-0410-883f-9ebac64fc565