v2c

Started from v2a, which was pulled from the pixel_level/src. Note that
v2b actually predated v2a, so kind of a misnomer.

Changes:
• enkf.f90: removed code to write out tbraw.out… this is unreliable as
it’s accessed from all processors
• enkf.f90: changed to only open the unit 9 file (tbraw_t.out) on the
head node. if you don’t do this, you create blank files on the slave
nodes, which (at least in my case) were sometimes copied back to the
run directory, which is bogus