Added streams to stop files from being uploaded if any files in that fol...

...der exists.

If a file does exist in s3, pipe a null variable to gulp-s3 in which it will fail and generate an error. Once it does, nothing will get uploaded.

This is not final, code still requires cleanup.
This function name, `wrapStreamIntoCheckS3Repo`, doesn't seem to fit very well.  It's doing a lot more than just wrapping a stream.  In fact, `stream` isn't even used, so I'd argue it's not even wrapping stream at all :).