All cosmeticomments fixed

Renamed sparsegrad to sparse_grad. Also imported spare module . Do a lazy import so perf is not hurt. 

 set the Theano flag warn.subtensor_merge_bug to False.
..........K......K..................................................................................................................................................................SS...SSSSS..........K.............................................
----------------------------------------------------------------------
Ran 2145 tests in 614.237s

OK (KNOWNFAIL=17, SKIP=47)
(theano-vivek)vvkulkarni@descartes:~/polyglot/polyglot/snippets$ python sparse.py 
******Testing advanced and sparse indexing***********
Using advanced Indexing
Time for Forward Pass:  0.201604127884
Time for Backward Pass:  0.73121881485
-----------------------------------------------------
Using sparse indexing
Time for Forward Pass:  0.378625154495
Time for Backward Pass:  5.72273588181
Test Passed
(theano-vivek)vvkulkarni@descartes:~/polyglot/polyglot/snippets$