Make stack-traces in node_modules configurable

[raadad]

As of Mocha 2.2.2 558191d@a8mfeat(runner/stack-trace): solve issue #545 + tes - lines 6358-63560

Errors that occur inside node_modules are not shown, this may not be ideal for people who are testing code that is running with node_modules or running a full stack test suite as the stack traces do not show.

Let me know your thoughts, i'm happy to PR a way to make this configurable.

[twada]

@raadad You can use --full-trace option to display full stack traces.

(Also found that Mocha site doesn't have documents for --full-trace option. It's another problem.)

[raadad]

I have confirmed this to be functioning, thanks for the quick response