add caches to theano_code interface
add relationals to sympy-theano translation
add Piecewise-switch sympy-theano translation
theano-Piecewise returns nan if no condition matches
standardize numpy import in test_theanocode
each call to theano_function runs on separate cache
Merge pull request #2366 from mrocklin/theano-piecewise

Theano Piecewise