Sync version number with the current CVS version.

(Note that the docs are also being maintained on the 2.1.1 maintenance
 branch, so users interested only in corrections and clarifications
 can get that.)

Doc/Makefile

@@ -67,7 +67,7 @@ TOOLSDIR=	tools
 
 # This is the *documentation* release, and is used to construct the file
 # names of the downloadable tarballs.
-RELEASE=2.1
+RELEASE=2.2a0
 
 PYTHON=	   python
 DVIPS=	   dvips -N0 -t $(PAPER)