Attempt at supporting nek's multi-file output (with directories).

This commit is broken; I am using it to relocate changes to a local
machine for debug.
Improving support for nfiles != 1.

nek-analyze now finds output files fo both nfiles < 0 and nfiles > 1.

If multiple threads are being used, they will be assigned to multiple
files to minimize the number of threads accessing each file.
Added zslice to npz save file.  Removed duplicate processing.
Memory improvements to procs.py and other cleaning.
Merge branch 'multi_file_input'

Conflicts:
	RTI/single_post.py
Just spacing