stereo_mpi: Use poll instead of wait

Not all stereo_corr jobs are the same. We need to poll around to see
what process we can pop. Life would be much easier if we could use
python multiprocessing ... but it is not available in 2.4.
asp: Make compliant with changes to IP matcher in VW

We dropped the argument that describes if we are bidirectional or
not. It now happens in the matcher's constructor. (Where it probably
should have always been).
IsisIO: Remove Isis headers from IsisCamera header

This should allow us to build against Isis camera models without
having to reference Isis Headers and all their ugly header
dependencies. You still need to link Isis and Isis dependencies. Just
not the headers!