redmine4094: Infer start-time from elapsed when needed.

Some variants of ps report start-time as a date if before today (no
matter how recently today started) or even report a year for dates
before this year (even if new year's day started mere seconds ago).
These, naturally, give very imprecise information.  When that happens
but we have an elapsed time column (containing a value we can parse),
use this to infer a better start-time.  At the same time, improve
parsing of relevant time strings generally.  Based on a patch from
Tony Lill - many thanks.

Added an acceptance test.  Failed before the fix, passes with it :-)
Use ``$(G.ps)``, not ``/bin/ps``, and add ``ps`` to the command list in ``dcs.cf.sub``.

Also, is this test supposed to pass on non-Linux platforms? ``ps`` is very non-portable in its arguments, Windows certainly won't pass, and commercial Unixes may also have trouble with some of the arguments.