Join methods for WidePanel
e.g.

def create_panels_join(a, b):
       """ return a join of the 2 panels """
       d = dict([ (i,(a[i].T.join(v.T)).T) for i, v in b.iteritems() ])
       return p.WidePanel.fromDict(d)
# this is a 'more' correct version, but have to assure that a[i] is not None

def create_panels_join(a, b):
        """ return a join of the 2 panels """
        items = set(a.items) + set(b.items)
        WidePanel.fromDict(dict([ (i,(a[i].T.join(b[i].T)).T) for i in items ]))
