Sync with branch-2.9.

- Added _SWSTR EPICS record for each filter module. This provides a string representation
  of filter module switch states.
- Modified display of filter module switch settings in SDF Diff table to use new record.
- Added some more error checking to SDF code.


git-svn-id: https://redoubt.ligo-wa.caltech.edu/svn/advLigoRTS/trunk@3970 6dcd42c9-f523-4c6d-aada-af552506706e