test suite: bail out on python versions << 2.4

The test suite uses function that were introduced in Python 2.4 (e.g.
set(), sorted()).

archivemail.xml

@@ -570,7 +570,7 @@ Also, there exist broken servers which do not implement server side searches.
 (<citetitle>Internet Message Format</citetitle>) rules for the
 <token>local-part</token> of email addresses in mind.
 So, rather than enforcing an <acronym>URL</acronym>-style encoding of
-non-<acronym>ascii</acronym> and reserved characters, it allows to
+non-<acronym>ascii</acronym> and reserved characters, it allows you to
 double-quote the username and password.
 If your username or password contains the delimiter characters
 <quote>@</quote> or <quote>:</quote>, just quote it like this:

test_archivemail

@@ -30,12 +30,12 @@ TODO: add tests for:
 import sys
 
 def check_python_version(): 
-    """Abort if we are running on python < v2.3"""
-    too_old_error = "This test script requires python version 2.3 or later. " + \
+    """Abort if we are running on python < v2.4"""
+    too_old_error = "This test script requires python version 2.4 or later. " + \
       "Your version of python is:\n%s" % sys.version
     try: 
         version = sys.version_info  # we might not even have this function! :)
-        if (version[0] < 2) or (version[0] == 2 and version[1] < 3):
+        if (version[0] < 2) or (version[0] == 2 and version[1] < 4):
             print too_old_error
             sys.exit(1)
     except AttributeError: