Switch default from forced exit to no-exit

[ScottFreeCode]

Allows --exit to override and force exit as before. Resolves #2879

[coveralls]

Coverage remained the same at 89.177% when pulling a3e32de on issue/2879 into 8b79c5d on master.

[coveralls]

Coverage remained the same at 89.177% when pulling 2b6991f on issue/2879 into 0f816ac on master.

[boneskull]

Please ensure browser users can do this too somehow

[boneskull]

Also, wait, does this actually work, just by changing it like that?

[ScottFreeCode]

This doesn't affect the browser one way or the other as it's purely the Node CLI process.exit call.

[ScottFreeCode]

And yeah, I think so -- just alter the Commander line and it switches the default value.

[coveralls]

Coverage remained the same at 89.436% when pulling 69c1e54 on issue/2879 into c5d69e0 on master.