Pause pyplot in nfq.py so plot is actuall updated.

On my machine, in the nfq.py example, with render = False, the pyplot
plot never appeared. To fix this, I put in a very short pyplot pause.
Now, the plot is updated in every iteration of the while-loop.
Merge branch 'master' of git://github.com/pybrain/pybrain into nfqplotting
Add a comment to nfq.py to describe my recent addition.
Merge pull request #112 from chrisdembia/nfqplotting

Fix pyplot issue in nfq example.