Remove bool argument, use a class to handle that.

enable v2 automatically sets using cudnn-batch norm.

"fix gen list"

Make PADDLE_ENFORCE and PADDLE_THROW catchable

Feature/middle level net api

Make C lib in `paddle.v2.master.client` lazy load

* Use EnforceNotMet to unify all exception types.

Add ImageExpandFunction.

Make implement an operator less noisy.

Fix hl_sequence_avg_forward.

Currently, WITH_GOLANG is a compiling flag, and not all Paddle binary
enable `WITH_GOLANG=ON`. So we cannot ensure that every paddle has
`master.so`. Make load that C libary lazily could let the user run
Paddle without `WITH_GOLANG=ON`.