Add tcp port 80 test

* src/pf/codegen.lua: Add a test.
Fix scoping of generated code

* src/pf/codegen.lua: Nest the expressions in scopes so that we don't
  jump into the middle of some local's scope.
Fix parsing of parenthesized expressions.

* src/pf/parse.lua: Parenthesized expressions can be logical or
  arithmetic.  Messily deal with this.
Fix not, and expansion

* src/pf/expand.lua: Fix expansion of not, and, etc.
Beginnings of new compiler tests

* src/pf.lua: Wire up the new compiler.