[Bug] rsync_project exclude flag broken in Python3+

Python3 added the __iter__ attribute to strings so the following check doesn't work:

Lines 107 to 108 in 8cff965

    
           if not hasattr(exclude, '__iter__'): 
        
               exclude = (exclude,)

This results in the exclude rsync flag splitting up a string like HELLO into H E L L O.

Looking at the newer Fabric's rsync they do the following:

With six.string_types switching depending on whether they are using Py3 or 2:

An easy workaround for now is to either move the exclude arguments into the extra_opts flag or to do exclude=["single-string"]

Thanks for the report!