Acknowledge the existence of the 'platform' file, generated by the
Makefile and used by the setup.py script.  Ignore it in .cvsignore;
remove it in "make clobber".
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 0354849..c6a053e 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -763,7 +763,7 @@
 	-rm -f $(PYTHON) $(PGEN) $(LIBRARY) $(LDLIBRARY) $(DLLLIBRARY) \
 		tags TAGS \
 		config.cache config.log config.h Modules/config.c 
-	-rm -rf build
+	-rm -rf build platform
 
 # Make things extra clean, before making a distribution:
 # remove all generated files, even Makefile[.pre]