Fix needing to rerun cargo on each koan

build.rs

@@ -1,8 +1,20 @@
 use std::fs::{OpenOptions};
+use std::io::{Write,ErrorKind};
 
 fn main() {
-    OpenOptions::new().create(true)
+    let path = OpenOptions::new().create_new(true)
         .write(true)
-        .open("src/path_to_enlightenment.rs")
-        .unwrap();
+        .open("src/path_to_enlightenment.rs");
+
+    match path {
+        Err(error) => {
+            match error.kind() {
+                ErrorKind::AlreadyExists => {},
+                _ => panic!("{}", error),
+            }
+        },
+        Ok(f) => {
+            write!(&f, "koan!(\"the_truth\");\n").unwrap();
+        },
+    }
 }

src/main.rs

@@ -50,6 +50,11 @@ fn seek_the_path() -> bool {
 
 #[cfg(not(test))]
 fn walk_the_path() -> bool {
+    Command::new("cargo")
+        .arg("clean")
+        .status()
+        .unwrap()
+        .success();
     Command::new("cargo")
         .arg("test")
         .arg("-q")