Added condition to Allocate nodes to support (conditionally) unused allocations.
Reverted some unnecessary changes.
Added condition to Realize nodes.
Fixed Allocate handler for C codegen to respect conditional allocations.
Simpler implementation of Allocate handler.
More clear implementation of Allocate/Realize handlers.
Simplified codegen for conditional Allocates.
Merge branch 'allocate_conditions' of https://github.com/halide/Halide into allocate_conditions
Not necessary to trace condition of Realize.
Merge pull request #356 from halide/allocate_conditions

Explicit Allocate and Realize conditions