Add example based tests, and fix python2 test
Add example based tests, and fix python2 test

* Added example based tests for slicing.
* Attempted fix for python2 tests. Now equality test is just skipped where length argument for slice.indices is negative, since it returned nonsense results in python2. See https://bugs.python.org/issue14794, in particular https://bugs.python.org/issue14794#msg174678

stonebig/numba,numba/numba,seibert/numba,seibert/numba,gmarkall/numba,gmarkall/numba,cpcloud/numba,sklam/numba,IntelLabs/numba,IntelLabs/numba,numba/numba,sklam/numba,sklam/numba,cpcloud/numba,seibert/numba,IntelLabs/numba,stonebig/numba,stuartarchibald/numba,cpcloud/numba,stonebig/numba,seibert/numba,stuartarchibald/numba,sklam/numba,numba/numba,gmarkall/numba,stonebig/numba,stonebig/numba,cpcloud/numba,stuartarchibald/numba,gmarkall/numba,sklam/numba,stuartarchibald/numba,cpcloud/numba,stuartarchibald/numba,numba/numba,IntelLabs/numba,numba/numba,IntelLabs/numba,seibert/numba,gmarkall/numba