Two bubbles are evolved with an isentropic (or isothermal) stratified
background.  To make it easy to track the bubbles, they are given
different compositions from the background.  One of the bubbles has
the same gamma as the background the other has a different gamma.

To plot the bubbles together, use:

contour2.py --label1 "B" --label2 "C" --m1 0.001 --M1 1 --m2 0.001 --M2 1 B C plt0XXXX

where contour2.py can be found in the AmrPostprocessing directory.
