sharding's "id_chooser" really needs a query parameter added

[Former user]

As discussed in IRC, the id_chooser from ShardedSession is currently just passed the ident. id_choosers probably want more context, so they can figure out what space of id's they're choosing from.

Very straightforward patch attached.

[Mike Bayer]

thanks, patched in b01c63280e16cd549601fb91393acbff3695821a.