Support for (fn paramsType returnType) matching

which allows all Fist tests to pass again! Next up: variable binding.
Starting work on variable bindings

Plain OpsArith stuff works properly, but anything that uses GensData,
GensChannel, etc. still fails.
Slightly more working-ness

on variable binding: now with OpsArith, OpsTime, GensData, GensChannel
working.
Fixed bug in genPoisson

Parameter name mismatch :)
OpsFilterValue now working
OpsFilterTime working again