Remove redundant checking in typed load

Problem

When using typed load and `clojure.core/load` is correctly monkey patched, typed dependencies are
redundantly checked via:
1. Normal `check-ns`-style dependency checking, then
2. Evaluating `load` as part of evaluating a `ns` form triggers another typed load for the same namespace.

Solution

We assume if typed load is being used, then `load` is correctly monkey patched.

We add an extra var that indicates if we are currently in a typed load, which disables the first
situation (`check-ns`-style checking).

Pull request: 73
Commit: e7ec01
Version: 0.3.20