JSLint tests fail if JSHint is installed

[marcelgerber]

1. Install the JSHint extension
2. Run Tests > Extensions > JSLint

Result:
2 pass, 2 fail

Expected:
All should pass

[dangoor]

The right fix for this would be to only load default extensions in the test window.

[marcelgerber]

This works now, probably thanks to the multiple linters PR.
Closing.