Add style check, test, and code fixes for an else brace check.

python/tidy/servo_tidy/tidy.py

@@ -415,6 +415,7 @@ def check_rust(file_name, lines):
             (r"^&&", "operators should go at the end of the first line", no_filter),
             (r"\{[A-Za-z0-9_]+\};", "use statement contains braces for single import",
                 lambda match, line: line.startswith('use ')),
+            (r"^\s*else {", "else braces should be on the same line", no_filter),
         ]
 
         for pattern, message, filter_func in regex_rules:

python/tidy/servo_tidy_tests/rust_tidy.rs

@@ -41,6 +41,12 @@ impl test {
         let x = true;
         x
             && x;
+        if x {
+             ;
+        }
+        else {
+             ;
+        }
     }
 
 }

python/tidy/servo_tidy_tests/test_tidy.py

@@ -76,6 +76,7 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual('use &str instead of &String', errors.next()[2])
         self.assertEqual('use &T instead of &Root<T>', errors.next()[2])
         self.assertEqual('operators should go at the end of the first line', errors.next()[2])
+        self.assertEqual('else braces should be on the same line', errors.next()[2])
         self.assertNoMoreErrors(errors)
 
     def test_spec_link(self):