auto merge of #8563 : graydon/rust/2013-08-16-condition-tutorial, r=catamorphism

First cut of a tutorial on conditions.

cc: #6701

Author: bors

configure

@@ -740,6 +740,7 @@ do
     make_dir $h/test/doc-tutorial-macros
     make_dir $h/test/doc-tutorial-borrowed-ptr
     make_dir $h/test/doc-tutorial-tasks
+    make_dir $h/test/doc-tutorial-conditions
     make_dir $h/test/doc-rust
 done