Make librustc_mir pass rustdoc

Author: Manishearth

src/librustc_mir/traversal.rs

@@ -19,13 +19,16 @@ use rustc::mir::repr::*;
 /// Preorder traversal is when each node is visited before an of it's
 /// successors
 ///
+/// ```text
+///
 ///         A
 ///        / \
 ///       /   \
 ///      B     C
 ///       \   /
 ///        \ /
 ///         D
+/// ```
 ///
 /// A preorder traversal of this graph is either `A B D C` or `A C D B`
 #[derive(Clone)]
@@ -80,13 +83,17 @@ impl<'a, 'tcx> Iterator for Preorder<'a, 'tcx> {
 /// Postorder traversal is when each node is visited after all of it's
 /// successors, except when the successor is only reachable by a back-edge
 ///
+///
+/// ```text
+///
 ///         A
 ///        / \
 ///       /   \
 ///      B     C
 ///       \   /
 ///        \ /
 ///         D
+/// ```
 ///
 /// A Postorder traversal of this graph is `D B C A` or `D C B A`
 pub struct Postorder<'a, 'tcx: 'a> {
@@ -215,13 +222,16 @@ impl<'a, 'tcx> Iterator for Postorder<'a, 'tcx> {
 /// This is different to a preorder traversal and represents a natural
 /// linearisation of control-flow.
 ///
+/// ```text
+///
 ///         A
 ///        / \
 ///       /   \
 ///      B     C
 ///       \   /
 ///        \ /
 ///         D
+/// ```
 ///
 /// A reverse postorder traversal of this graph is either `A B C D` or `A C B D`
 /// Note that for a graph containing no loops (i.e. A DAG), this is equivalent to