Let sourcemaps be cached

[kulshekhar]

This change allows source-map-support to use the default value for emptyCacheBetweenOperations (false) to improve the performance of ts-jest.

Thanks to @hermanbanken for pointing out this issue in #259

[GeeWee]

Do we need to test jest multiple times in sequence to ensure this doesn't break e.g. --watch?

[kulshekhar]

Do we need to test jest multiple times in sequence to ensure this doesn't break e.g. --watch?

Sounds like a good idea. I'm not yet sure how to automate that though

Edit: A simple test showed this worked (displayed changed line numbers) with --watch

Edit 2: It looks like we're already testing this 😄

[GeeWee]

I'm not sure about that either.
Just to be clear - did you pull this branch into a regular project and test it, or how did you test it?

[kulshekhar]

I'm not sure about that either.

I just updated my comment above. We're already testing this.

Just to be clear - did you pull this branch into a regular project and test it, or how did you test it?

I used the project linked from #259 to test this by changing the file in the ts-jest source in node_modules

[GeeWee]

Damn, past us are smart people..!
Let's merge this baby in.