The name of the stack distance stats changed slightly when the stack
distance calculator was redesigned as a probe. Update the reference
stats to reflect this.
Apparently only stats.txt was updated the last time, so
this changeset updates other reference output files
(config.ini, simout, simerr, ruby.stats) so that
test output diffs should not be cluttered with irrelevant
changes. There are a few stats.txt updates too, but
they are in the minority.
