Added MultipleFileUpload step.

Use this to upload multiple files at once. Supports all the options of
FileUpload and DirectoryUpload. Makes use of the "stat" command to
determine the kind of file that is uploaded. "Skips" if slavesrcs is an
empty list. "slavesrcs", "masterdest" and "url" are renderable.

    transfer.MultipleFileUpload(slavesrcs=['some/file', 'some/directory'],
                                masterdest='targetdir')
Refactored FileUpload test
Type (timestamp -> srctimestamp)

Yikes! Thank you, Travis!
obligatory pep8 commit
Manual, release notes for MultipleFileUpload