Fix out-of-bounds indexing into PVT function table

The 'props_' table of PVT functions has one entry for each active
phase.  Fix four instances of indexing into the table using the
canonical rather than active phase indices.

This is necessary, but not sufficient, to run two-phase problems
without a "dummy" third phase.
Merge pull request #204 from bska/fix-oob-pix

Fix out-of-bounds indexing into PVT function table