Add warning to Seq __hash__ like that for __cmp__

Suggested by Sergei Lebedev via Twitter.
Use list in order to avoid hash of Seq object.

Current code was implicitly assuming Seq hashing using
object comparison, but we're planning to make that use
sequence string comparison instead. See Bio/Seq.py
Clearer TogoWS test error
TogoWS currently not offering omin database :(