Email validator: don't allow multiple hostnames

In addition to not allowing `@` multiple times in the string, we're now
checking that the *entire* string matches our regex - previously, you could
tack on anything to the end of a valid email address and have it succeed.

r2/r2/lib/validator/validator.py

@@ -2070,7 +2070,7 @@ class ValidEmails(Validator):
     success"""
 
     separator = re.compile(r'[^\s,;]+')
-    email_re  = re.compile(r'[^\s]+@[^\s]+\.[^\s]+')
+    email_re  = re.compile(r'\A[^\s@]+@[^\s@]+\.[^\s@]+\Z')
 
     def __init__(self, param, num = 20, **kw):
         self.num = num

r2/r2/tests/unit/lib/validator/test_validator.py

@@ -83,3 +83,6 @@ class TestValidEmail(unittest.TestCase):
         self.setUp()
         self._test_failure('@example.com')
 
+    def test_two_hostnames(self):
+        self._test_failure('test@example.com@example.com')
+