reformatting dfa.c, now is the time

[Jim Meyering]

Some recent review challenges have highlighted the need
for a consistent formatting style in dfa.c, and since the changes
Paul pushed today have touched so much of that file already,
this is probably the best time to make the code conform.
As far as I know, no one is carrying significant patches
against that file.  If you are, please speak up ASAP.
I'll probably simply filter it through indent --no-tabs.