heterodyne: Allow for absent JIGL_CNT header, defaulting to 5.

Also correct the comment directly above.
heterodyne: Protect both FINDBACK and FIXSTEPS for too few spectra.

This should have gone in last December to address fault 20121105.004.
When I introduced the ringing filter during my travels, it appears that I
adapted not the latest version but an older one (9080cddb519c23387).
heterodyne: Align code indentation.
heterodyne: Treat non-HARP frontends as a survey to permit QA constraints.

The default aka Telescope QA parameters are not suitable for receivers
like RxB.  A means to enable the qa.ini file can have sections such as
[RXB] was needed.

This implementation might be regarded as a fudge, but it seemed the
clearest way to adapt the existing code to permit QA parameter
settings for the DAS receivers, for which there was no survey.
heterodyne: Fix prologue typo'