[GSoC 2015 Week 5&6]

In the Week 5 and Week 6, I was working on a new feature for debugging, to display the names of rejected optimizers when doing "replace_and_validate()". The PR is here. 

To implement this feature in one place in the code, the python library "inspect" is used. Anytime validation fails, the code will inspect the current stack frames and get to know which optimizer is the caller and whether there is "verbose" flag. Then the information for debugging can be displayed.

Besides, optimization for the local_fill_sink optimizer is also began here, the main idea on local_fill_sink is to make "fill" to sink in a recursive way to be more efficiency. 

For the inplace_elemwise optimizer, it is not merged because of the bad performance.