gf.cabal, gf-server.cabal: add version bounds on network & httpd-shed

* httpd-shed-0.4 does not specify an upper bound on network, but it fails
  to build against network>=2.6. This is fixed in httpd-shed-0.4.0.2.
* With network-2.6, the Network.URI modules is moved to a separate package,
  so for the time being GF requires network>=2.3 && <2.6. This is compatible
  with the four most recent versions of the Haskell Platform.

src/server/gf-server.cabal

@@ -36,9 +36,9 @@ Library
                    process,
                    gf >= 3.6,
                    cgi >= 3001.1.7.3,
-                   httpd-shed,
+                   httpd-shed>=0.4.0.2,
                    mtl,
-                   network,
+                   network>=2.3 && <2.6,
                    json >= 0.3.3,
                    utf8-string >= 0.3.1.1,
                    bytestring,