changed find/rfind to return -1 for matches outside the source string
diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index 5fe9fb9..c2e0875 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -154,6 +154,10 @@
         self.checkequal(9, 'abcdefghiabc', 'find', 'abc', 1)
         self.checkequal(-1, 'abcdefghiabc', 'find', 'def', 4)
 
+        self.checkequal(0, 'abc', 'find', '', 0)
+        self.checkequal(3, 'abc', 'find', '', 3)
+        self.checkequal(-1, 'abc', 'find', '', 4)
+
         self.checkraises(TypeError, 'hello', 'find')
         self.checkraises(TypeError, 'hello', 'find', 42)
 
@@ -188,6 +192,10 @@
         self.checkequal(0, 'abcdefghiabc', 'rfind', 'abcd')
         self.checkequal(-1, 'abcdefghiabc', 'rfind', 'abcz')
 
+        self.checkequal(3, 'abc', 'rfind', '', 0)
+        self.checkequal(3, 'abc', 'rfind', '', 3)
+        self.checkequal(-1, 'abc', 'rfind', '', 4)
+
         self.checkraises(TypeError, 'hello', 'rfind')
         self.checkraises(TypeError, 'hello', 'rfind', 42)