Bug fix phi_helper_omni()

The expertise sub-calculation was fouling the results for the PVE
calculation, both damage and healing.
Fixed by adding an edge case, much like for alacrity.

Also added a new inequality to get_h().
This uses the average of the stats, and is both too restrictive,
and likely not very accurate.
However, the results so far are more in line with reality.
Needs more tweaking.