Fixes cleanup issues and improves cleanup logic.

[kwmsmith]

Caught some big cleanup bugs -- this fixes them.

[cowlicks]

What were there bugs?

[cowlicks]

Ah the applysync __name__ thing? Okay, I think this is ready to merge once it is rebased.

[kwmsmith]

On master, if I run the testsuite and then run the following, it indicates that there are still distarray objects on the engines:

# dump_cluster.py
from __future__ import print_function
from IPython.parallel import Client

c = Client()
dv = c[:]

def count(prefix):
    keys = 0
    for k in globals():
        if k.startswith(prefix):
            keys += 1
    return keys

print(dv.apply_async(count, '__distarray__').get_dict())

The output I get is:

$ python dump_cluster.py
{0: 2102, 1: 1927, 2: 1754, 3: 1680}

After applying this PR, I get zeros for the counts, as it should be.

[kwmsmith]

@cowlicks merged in master -- this one's ready for merging.

[cowlicks]

Looks good, I think. Its hard to tell what merging in master actually did since those commits contain so much unrelated stuff.