this enables to do multi-detector trigger generator & coincidence analysis
by inputs of channel-name, data, template, and PSDs from multiple IFOs.
In short, this is lalapps_StringSearch + ligolw_add + lalapps_burca of old pipeline.

like the old burca

__lt__() and friends

Add explicit synchronization point.

See merge request lscsoft/gstlal!10

dagparts.py: add cache_to_instruments(), used in group_T050017_filename_from_T050017_files() to fix bug repeating same ifo when used repeatedly

gstlal_compute_strain:  Now allows the updating of line frequencies in the general line subtraction code.

If there's a large number of parent / child relationships, instead
of having a set of all-to-all arcs (which can number into the tens
of millions for many parents and children in one line), add in a
explicit no-op node.  This causes the number of arcs to grow linearly
instead of quadratically.

HTCondor will do this automatically in future versions; this commit
should be reverted once the new dagman is available.