stereo: Remove reference to nadirpinhole session

We're not ready to document and it is still research code.
Sessions: Fix includes inside StereoSession.cc

This brings in asp_config.h which gives access to determining if we
are built with ISIS support.
stereo: Correct argument parsing in response to f0be116

We no longer no what the session type is at this point.
Session: Robustify session guessing

As soon as we find one that sticks, go with it to the end.
stereo: Stereo Session Str is not a reliable indicator of Session

Instead use session->name() to determine who is operating.
RPC: Have RPC session use specialized RPCStereoModel

Whoops! I forgot to implement this in the rewrite. Funny thing was
that I planned for it.