implement MultiTransferException::getExceptionForFailedRequest($req) to identify which exception caused which request to fail
Tidying up the exception updates
Fix fatal error in RequestMediator::writeResponseBody() when malformed response is recieved

https://github.com/guzzle/guzzle/issues/408
Minor tweak
Only exploding on header glue when not inside of a comma. Closes #411
Making mimetype guessing case-insensitive
Removed guessing of request body content type by request path. Reverts part of 863998bb.