#41 source transformers for recursion

[mminder]

We are using React in our project. .jsx files need to be transformed to .js files. It is not enough to transform the file under test, also other .jsx files required by the file under test need to be transformed.

This minimal change would allow this and fix issue #41 .

[domenic]

Nice!

I'd like to flip the configuration around a bit, if you don't mind:

• Add a new option, sourceTransformersSingleOnly, which if undefined is set equal to options.singleOnly (otherwise converted to a boolean).
• Update the test to not pass any options besides sourceTransformers
• Add another test (or modify an existing one?) showing that singleOnly: true will turn off recursive source transformers
• Add a third test showing that sourceTransformersSingleOnly: true will turn off recursive source transformers but not recursive sandboxing.

If we can manage this then I'll release a 2.0.0 with the new defaults.

[mminder]

Ok, I did the changes. hope I understood you correctly ;) Otherwise feel free to comment or change my code.

[domenic]

Thanks! Merged as 16136b82ffa065aca4217ab7cf31a2751ce496b5 with some follow-up tweaks in b029c26ae3cb2f3ae69d8b52a91045832539f785