[Yt-dev] Module renames

[Stephen Skory]

In svn (1744), and in yt-doc (9854b43eedcc) I renamed and changed all mentions of 

MergerTree.py -> merger_tree.py
HaloMassFcn.py -> halo_mass_function.py


 _______________________________________________________
sskory at physics.ucsd.edu           o__  Stephen Skory
http://physics.ucsd.edu/~sskory/ _.>/ _Graduate Student
________________________________(_)_\(_)_______________