Measuring the rates of success of predicates

[James Youngman]

I've added a new debug option, "-D rates" to find 4.3.x (the CVS code
only, so far).  It displays the number of visits to each predicate and
how many times it succeeded.  You can use this in combination with "-D
opt" to figure out if the assumptions that find made about the
likelihood of each test succeeding were in fact right in real life.
These assumptions about success rates are used when optimising the
order of expression evaluation.

James.