When opening a file, check whether it is bad.  Presently the new function is_file_bad()
does a few checks on the axes.  More checks can be added as needed.
fix typo
Add metadiags.py script.
Also:
Some fairly minor usability changes -- realms now have a coords and filekey. added --xml option (primarily used in diags.py). added --outputpre/--outputpost options for tweaking filenames
icky hacks for questionable units in obs sets
Add TGCLDLWP->TGCLDLWP_OCEAN to the special vars; also stop printing varlist from amwg set 4
check for available sets vs user requested sets
oops typo
fix usage instructions