Changed linear solver to use expr_uses_vars function rather than a custom version of the same. Minor style tweaks as well.
Changed linear solver to use expr_uses_vars function rather than a custom version of the same. Minor style tweaks as well.


Former-commit-id: 603e67f9964d38e15599b51e5f179e8f31679c3b
darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide