Issue #27626: Spelling fixes in docs, comments and internal names

Based on patch by Ville Skyttä.
diff --git a/Demo/tix/samples/BtnBox.py b/Demo/tix/samples/BtnBox.py
index af2a2a8..d5e2e29 100644
--- a/Demo/tix/samples/BtnBox.py
+++ b/Demo/tix/samples/BtnBox.py
@@ -2,7 +2,7 @@
 #
 # $Id$
 #
-# Tix Demostration Program
+# Tix Demonstration Program
 #
 # This sample program is structured in such a way so that it can be
 # executed from the Tix demo program "tixwidgets.py": it must have a