needless_continue: Add ui test

The test program contains both conditions tested by the lint, i.e.,
a redundant continue in the `if` and `else` blocks within a loop. Maybe
splitting them out and also having a program that should *not* trigger
the lint warning is better.

tests/ui/needless_continue.rs

@@ -0,0 +1,50 @@
+#![feature(plugin)]
+#![plugin(clippy)]
+
+macro_rules! zero {
+    ($x:expr) => ($x == 0);
+}
+
+macro_rules! nonzero {
+    ($x:expr) => (!zero!($x));
+}
+
+#[deny(needless_continue)]
+fn main() {
+    let mut i = 1;
+    while i < 10 {
+        i += 1;
+
+        if i % 2 == 0 && i % 3 == 0 {
+            println!("{}", i);
+            println!("{}", i+1);
+            if i % 5 == 0 {
+                println!("{}", i+2);
+            }
+            let i = 0;
+            println!("bar {} ", i);
+        } else {
+            continue;
+        }
+
+        println!("bleh");
+        {
+            println!("blah");
+        }
+
+        // some comments that also should ideally be included in the
+        // output of the lint suggestion if possible.
+        if !(!(i == 2) || !(i == 5)) {
+            println!("lama");
+        }
+
+        if (zero!(i % 2) || nonzero!(i % 5)) && i % 3 != 0 {
+            continue;
+        } else {
+            println!("Blabber");
+            println!("Jabber");
+        }
+
+        println!("bleh");
+    }
+}

tests/ui/needless_continue.stderr

@@ -0,0 +1,66 @@
+error: This else block is redundant.
+
+  --> $DIR/needless_continue.rs:26:16
+   |
+26 |           } else {
+   |  ________________^ starting here...
+27 | |             continue;
+28 | |         }
+   | |_________^ ...ending here
+   |
+note: lint level defined here
+  --> $DIR/needless_continue.rs:12:8
+   |
+12 | #[deny(needless_continue)]
+   |        ^^^^^^^^^^^^^^^^^
+   = help: Consider dropping the else clause and merging the code that follows (in the loop) with the if block, like so:
+           if i % 2 == 0 && i % 3 == 0 {
+               println!("{}", i);
+               println!("{}", i+1);
+               if i % 5 == 0 {
+                   println!("{}", i+2);
+               }
+               let i = 0;
+               println!("bar {} ", i);
+           
+               // Merged code follows...
+               println!("bleh");
+               {
+                   println!("blah");
+               }
+               if !(!(i == 2) || !(i == 5)) {
+                   println!("lama");
+               }
+               if (zero!(i % 2) || nonzero!(i % 5)) && i % 3 != 0 {
+                   continue;
+               } else {
+                   println!("Blabber");
+                   println!("Jabber");
+               }
+               println!("bleh");
+           }
+           
+
+error: There is no need for an explicit `else` block for this `if` expression
+
+  --> $DIR/needless_continue.rs:41:9
+   |
+41 |           if (zero!(i % 2) || nonzero!(i % 5)) && i % 3 != 0 {
+   |  _________^ starting here...
+42 | |             continue;
+43 | |         } else {
+44 | |             println!("Blabber");
+45 | |             println!("Jabber");
+46 | |         }
+   | |_________^ ...ending here
+   |
+   = help: Consider dropping the else clause, and moving out the code in the else block, like so:
+           if (zero!(i % 2) || nonzero!(i % 5)) && i % 3 != 0 {
+               continue;
+           }
+           println!("Blabber");
+           println!("Jabber");
+           ...
+
+error: aborting due to 2 previous errors
+