IDLE: Fix 2 typos found by Min ho Kim. (GH-15617)

Lib/idlelib/README.txt

@@ -115,7 +115,7 @@ tooltip.py # unused
 
 IDLE MENUS
 Top level items and most submenu items are defined in mainmenu.
-Extenstions add submenu items when active.  The names given are
+Extensions add submenu items when active.  The names given are
 found, quoted, in one of these modules, paired with a '<<pseudoevent>>'.
 Each pseudoevent is bound to an event handler.  Some event handlers
 call another function that does the actual work.  The annotations below

Lib/idlelib/browser.py

@@ -29,7 +29,7 @@ def transform_children(child_dict, modname=None):
     The dictionary maps names to pyclbr information objects.
     Filter out imported objects.
     Augment class names with bases.
-    The insertion order of the dictonary is assumed to have been in line
+    The insertion order of the dictionary is assumed to have been in line
     number order, so sorting is not necessary.
 
     The current tree only calls this once per child_dict as it saves