Add a 'test verifier' sub-test.

This test runs the verifier on each function and matches the resulting
verifier error against the "error:" annotation.

Move the existing verifier test into filetests/verifier/ and use the new
syntex.

src/tools/filetest/subtest.rs

@@ -13,10 +13,12 @@ pub fn new(parsed: &TestCommand) -> Result<Box<SubTest>> {
     use cat;
     use print_cfg;
     use filetest::domtree;
+    use filetest::verifier;
     match parsed.command {
         "cat" => cat::subtest(parsed),
         "print-cfg" => print_cfg::subtest(parsed),
         "domtree" => domtree::subtest(parsed),
+        "verifier" => verifier::subtest(parsed),
         _ => Err(format!("unknown test command '{}'", parsed.command)),
     }
 }