gstlal_inspiral_plotsummary: make a command line option for the far threshold to discern found injections

datasource.py: set seg in GWDataSourceInfo to None, seive cache src field on first letter of instrument

lloidparts: port LLOID fully to use datasource module, TODO SPIIR port and removal of mkLLOIDsrc() in LLOID, i.e. full port to multirate_datasource module

- framecpp_muxcollectpads_get_common_span() and
  framecpp_muxcollectpads_get_span() are added.

- this required reworking the locking.  the collectpads object lock is now
  aquired and held throughout event pad sink handling (so the aquisition of
  the lock had to be removed from channelmux's sink event handler), and the
  collectpads' pad list lock's aquisition is pushed down into lower-level
  functions so that several different code paths can aquire and release it
  without collision.

- make actual *playback* a possibility
- document allowed output formats in help message
- make whitening optional
- if both low- and high-pass filtering are on use a single band-pass filter
- add an amplification option
- allow the sample rate to be controlled from the command line
- add extra error checking