Add some "used with permission" mentions where external resources are referenced.

Permission was validated prior to adding these markings.

Lib/datetime.py

@@ -896,6 +896,7 @@ class date:
 
         ISO calendar algorithm taken from
         http://www.phys.uu.nl/~vgent/calendar/isocalendar.htm
+        (used with permission)
         """
         year = self._year
         week1monday = _isoweek1monday(year)

Lib/encodings/hp_roman8.py

@@ -5,6 +5,8 @@
     Original source: LaserJet IIP Printer User's Manual HP part no
     33471-90901, Hewlet-Packard, June 1989.
 
+    (Used with permission)
+
 """#"
 
 import codecs

Lib/unittest/__init__.py

@@ -1,6 +1,6 @@
 """
 Python unit testing framework, based on Erich Gamma's JUnit and Kent Beck's
-Smalltalk testing framework.
+Smalltalk testing framework (used with permission).
 
 This module contains the core framework classes that form the basis of
 specific test cases and suites (TestCase, TestSuite etc.), and also a