- remove entries referring to non-existing stuff
- prefix files appearing in the top-level directory with '/'
- add '/' as suffix for directories
- add '*.mo' for files created during the test run
- sort the entries

We have to create a new XPath context for every rule, and we have
to freshly apply any ITS params to that context. But what we were
also doing is looking thru the children of the parent ITS rules
element for param element each time. This was inefficient. Looking
for param elements only once per ruleset gives a small but measurable
speed boost.

If these aren't explicitly set for a node with a selector or local markup,
then we have to chain up, often all the way to the root. But we were doing
this over and over again, chaining up across the same nodes. This change
stores the computed value, so chaining up usually hits that cache. I was
careful to clear the cache if new rules are applied.

In a recent commit for profiling, I moved the __main__ code to a main()
function. This broke some stuff that relied on an accidentally global
variable. Now the variable gets passed as a param, as it should.

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