dep_sort: disable fall through optimization

This seems to be producing bad results. One of the tests results was
checking for the wrong flowtable result. Once that was fixed, the test
started failing, but they pass when the fall through optimization is
disabled.
dep_sort: Add topological sort module
dep_sort: properly sort flows according to dependencies

The dependency relation among flows is a partial ordering. The code was
previously treating it as a total ordering, and was therefore producing
bogus results.
dep_sort: add all vertices to the topo graph
dep_sort: flip sign of compare
dep_sort: delay obscures calls
dep_sort: separate compare and dep_compare in functor

One is used for lookup tables, the other is used to determine the
partial order. dep_compare uses -1 for less than, 1 for greater than,
and 0 for incomparable.
Merge pull request #291 from frenetic-lang/dep_sort

Properly sort pattern/action before generating flowtables