Add a lint to suggest uint == 0 over uint <= 0

tests/compile-fail/absurd_unsigned_comparisons.rs

@@ -0,0 +1,14 @@
+#![feature(plugin)]
+#![plugin(clippy)]
+
+#![allow(unused)]
+
+#[deny(absurd_unsigned_comparisons)]
+fn main() {
+    1u32 <= 0; //~ERROR testing whether an unsigned integer is non-positive
+    1u8 <= 0; //~ERROR testing whether an unsigned integer is non-positive
+    1i32 <= 0;
+    0 >= 1u32; //~ERROR testing whether an unsigned integer is non-positive
+    0 >= 1;
+    1u32 > 0;
+}