[GSoC 2015 Week 2]

In the week 2 I implement one optimization to the Equilibrium Optimizer. The PR is here.

In this optimization, an "final optimization" procedure is added to the equilibrium optimization. Final optimizers is a list of global optimizers, and will be applied at the end of every equilibrium optimization pass. The number of optimization pass is expected to decrease, by making right optimizers final ones.

Another change is to delete a node's function graph reference when pruning it from a function graph. So merge optimizer can easily tell whether a node belongs to a graph. It will be useful in other optimizers too.

In the next week, the next 2 optimizations in the to-do list are what I'm going to do:

* Make local_dimshuffle_list lift through many elemwise at once
* Speed up inplace elemwise optimizer

Thanks. Any feedback is welcome!