Fix for inproper exit-code on spec failures

[CraZySacX]

This change should resolve issue #81 where lein spec was always exiting with an exit-code of 0. This should allow for proper CI integration. The exit-if-needed function appeared to always be receiving nil, and therefore evaluating to 0 in every case.

[CraZySacX]

Any chance on this getting in? I'm currently using my fork successfully with Travis, would be nice to be in master.

[sdegutis]

I would merge it, but I haven't fully looked through it yet to make sure I fully understand what it does in the patch and what it used to do. I'll try to look through it in the next few days. Hopefully I can do so before @slagyr cuts the next release.

[CraZySacX]

Sounds good, thanks. Let me know if you have any questions. Basically, in the before code, the exit-code was always evaluating to 0, which causes issues with CI systems that rely on a non-zero exit-code when errors occur. The new code evaluates to 0 if all the tests are successful, or evaluates to the number of failed tests (up to 250) if there are failures.