Added the start of a test for specialized branched loops.
Added the start of a test for specialized branched loops.

Highlights a bug where only the innards of the select are
preserved in the branched versions.


Former-commit-id: 7efbbc27c9066a0a00e0abf243330e57712c07ac
darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide