Added code to plot_mesh_tally.py which gives an option to plot mean or relative uncertainty.
Added the ability to plot absolute uncertainties in addition to mean and relative.
Removed python2 from the usr/bin/env statement and replaced with just python. (putting it back the way it was)
Merge pull request #181 from nelsonag/relunc_plot

Added code to plot_mesh_tally.py which gives an option to plot mean or r...