Bump version number.
diff --git a/Doc/Makefile b/Doc/Makefile
index 1e51903..6732b64 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=2.2a3
+RELEASE=2.2a4
 
 PYTHON=	   python
 DVIPS=	   dvips -N0 -t $(PAPER)