Added a complex multi-stage reduction test.
Added a complex multi-stage reduction test.

It recursively expands its bounds.


Former-commit-id: 9f81cae14f73cf405f4692065344d3a1d5e2e82c
darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide