Don't rewrite let-open expressions
Don't rewrite let-open expressions

Summary: Rather than always using `Module.(...)` (which can add a lot of indentation), allow the user to write either that or `let open Module in` as they wish and preserve what is written.

Reviewed By: gabelevi, mvitousek, nmote, dsainati1, vrama628

Differential Revision: D17675693

fbshipit-source-id: eaf6770288074d9842ad7ada5f73f00b84b95a1b

gabelevi/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,mroch/flow,facebook/flow,samwgoldman/flow,gabelevi/flow,mroch/flow,facebook/flow,gabelevi/flow,gabelevi/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,gabelevi/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow,facebook/flow,samwgoldman/flow,gabelevi/flow,gabelevi/flow,mroch/flow