update io test to use tmp directory, and update configure to create it

Author: nikomatsakis

configure

@@ -349,7 +349,7 @@ step_msg "making directories"
 for i in \
     doc doc/std \
     nd nd/std \
-    dl
+    dl tmp
 do
     make_dir $i
 done

src/test/stdtest/io.rs

@@ -6,7 +6,7 @@ import std::result;
 
 #[test]
 fn test_simple() {
-    let tmpfile: str = "test/run-pass/lib-io-test-simple.tmp";
+    let tmpfile: str = "tmp/lib-io-test-simple.tmp";
     log tmpfile;
     let frood: str = "A hoopy frood who really knows where his towel is.";
     log frood;