handling unicode port names

[belevtsoff]

Calling workflow.connect(src, srcport, dst, dstport) with a unicode port name like srcport = u"in_file" causes an error, because of the isinstance(srcport, str) typechecking in the connect() code, which returns False for unicode strings. Is there any reason for not supporting such strings? If not, I'll submit a pull request fixing it

[chrisgorgo]

there is no reason not to support unicode; a PR would be much appreciated