gf.cabal: bump version to 3.2.8-darcs

This is just to make it easier to tell who has the latest version at the 
summer school. There has been some bug fixes in gf itself and some significant
additions to the RGL since 3.2 was released.

Also explicitly require Alex 2.x. The recently released Alex 3.0 has backwards
incompatible changes and does not work. GF/Grammar/Lexer.x should probably
be modified to support both Alex 2.x and Alex 3.0...

gf.cabal

@@ -1,5 +1,5 @@
 name: gf
-version: 3.2.1-darcs
+version: 3.2.8-darcs
 
 cabal-version: >= 1.8
 build-type: Custom
@@ -90,7 +90,7 @@ executable gf
     build-depends: httpd-shed, network, silently, utf8-string
     cpp-options: -DSERVER_MODE
     other-modules: GFServer
-  build-tools: happy, alex
+  build-tools: happy, alex>=2 && <3
   if os(windows)
     build-depends: Win32
   else