Add display test for range args

Author: CraftSpider

src/test/rustdoc/range-arg-pattern.rs

@@ -0,0 +1,5 @@
+#![crate_name = "foo"]
+
+// @has foo/fn.f.html
+// @has - '//*[@class="rust fn"]' 'pub fn f(0u8 ...255: u8)'
+pub fn f(0u8...255: u8) {}