Fixes checkpoint time calculation from m to s
Reverts farm option 'memory_mb' back to 'memory'
Changes default checkpoint rate to 0.15 s/MB
Returns to Sanger farm3 queue limits

And adds runtime_limit_seconds which can be specified as a limit to enable
use of -W limits in LSF.
Changes new runtime limit to use -We instead of -W

LSF was being to viciously murderous in killing off jobs that were
in the middle of checkpointing.  Now using -We as an estimate, and
killing the job ourselves after the runtime has elapsed and the
latest checkpoint is done.
Fixes regex capture of RUNTIME
Changes minimum checkpoint period to 1 minute
Fixes bug wherein some jobs would be restarted & submitted from start