Add extension paths to TestDiscoverers

Need this in an upcoming change
Only remove extension directories on real failures

This is to aid Issue #4 SUPERBODGE where we force-failures to get test
locations
When listing tests, if we have stack traces but no location, attempt to parse them

This is part of Issue #4 SUPERBODGE
Force tests to fail if we're requests lists, so we can get filename/line number

Part of Issue #4 SUPERBODGE