Added warning for pressure in geotherm

Pressures outside of PREM should not be evaluated for temperatures
Added geotherm tests

Goetherm tests added
Added Negative Pressure warning

Negative pressure warning, cleanup
Added warning and fixed broken line in previous commit

Added depth warning for B&S81 and fixed a tab (spaces) error
Added to test.py

Added to test.py
Fixed broken partitioning test

partitioning was broken, now it’s fixed.
Merge pull request #69 from lordkman/test_geotherm

Test geotherm