adding advanced indexing to theano tensors
putting advance_indexing as part of the TestAdvancedSubtensor class
correcting the function call self.equal_slices
issue #1914, checking if a is an instance of slice.
issue #1914, changing the place of equal_slices method and making code adaptable with PEP8 formatting
Merge pull request #2162 from SinaHonari/issue1914

Issue1914