Add uncan_dict to uncan_map

[wilywampa]

This change is a result of investigating this StackOverflow question regarding parallel.Reference objects in a list of dictionaries: http://stackoverflow.com/questions/31343529/ipython-parallel-reference-with-map-vs-apply

from IPython import parallel
from IPython.parallel import Client
from IPython.parallel import Reference

rc = Client()
dview = rc.direct_view()
dview.block = True

dview['l'] = [0, 1]
kws = [{'l': Reference('l')}]
def second(kws):
    l = kws['l']
    return l[1]

dview.map(second, kws) # results in TypeError: 'Reference' object does not support indexing

When a list of dictionaries is provided as an argument to a parallel map, the Reference objects in the dicts aren't reached by the uncan function. Adding dict to the list of uncanners produces the correct behavior:

>>> dview.map(second, kws)
[1]