utils.time: Add support for timezones without a slash.

eg. UTC, CET, ...

plugins/Time/test.py

@@ -96,6 +96,7 @@ class TimeTestCase(PluginTestCase):
     def testTztime(self):
         self.assertNotError('tztime Europe/Paris')
         self.assertNotError('tztime America/Indiana/Knox')
+        self.assertNotError('tztime UTC')
         self.assertError('tztime Europe/Gniarf')
 
     @skipIf(not has_dateutil, 'python-dateutil is missing')

src/utils/time.py

@@ -41,7 +41,7 @@ try:
 except ImportError:
     pytz = None
 
-_IANA_TZ_RE = re.compile("([\w_-]+/)+[\w_-]+")
+_IANA_TZ_RE = re.compile("([\w_-]+/)*[\w_-]+")
 
 class TimezoneException(Exception):
     pass