This lower memory usage and speed up optimization by asking for less merge.

This make Merge Optimzer take 21s instead of 35s in one case.

I think this work correctly in case of revert.

[MRG]Deprecated

The NULL check was there before 4b4eeaad

Skip a test with python 2.4

Manually updated scan c code version too.

This simplify the *IncSubtensor code at the same time.

IncSugtensor and the GPU code still need update.

Fix grad of Alloc when we unbroadcast an input.