Issue with meshtal_combine.py

[makeclean]

I have issues when using the meshtal_combine script, I suspect its due to the variety of formats in meshtals. @zwelchWI I have emailed you a link (https://docs.google.com/file/d/0BzKVLkDlDJg4c0t6bWJHNnRqejg/edit?usp=sharing) to google drive to get the file I have problems with.

[gonuke]

Now that @elliottbiondo has put mesh tally into PyNE and is adding mesh tally math - we should consider refactoring this to be based on the PyNE capability.

Also - we should put it under CI on Batlab (my favorite thing to do these days!) :)