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/.cvsignore b/.cvsignore
index ceb8a91..4860994 100644
--- a/.cvsignore
+++ b/.cvsignore
@@ -8,3 +8,4 @@
 python
 build
 Makefile.pre
+platform