Use "2.1c1" since that is what Guido used for the Python version number.
diff --git a/Doc/Makefile b/Doc/Makefile
index a2da302..b8cc712 100644
--- a/Doc/Makefile
+++ b/Doc/Makefile
@@ -67,7 +67,7 @@
 
 # This is the *documentation* release, and is used to construct the file
 # names of the downloadable tarballs.
-RELEASE=2.1rc1
+RELEASE=2.1c1
 
 PYTHON=	   python
 DVIPS=	   dvips -N0 -t $(PAPER)