Stop wrapping/prepending error messages so that we do not loose the stack trace. For this, update a few manually thrown errors with better messages (usually including a file path).
Speed up locations by doing manual `sourceMapSupport.wrapCallSite()` for a single call site. Performance gain in the runner process with 100 files x 100 tests each:
- 25% on the fresh run without babel cache;
- 80% on the cached run where babel is almost instant.
Also some obvious cleanups around stack traces (removing unused code).
