Standalone HTTP version of pgf-server

pgf-server can now act as a standalone HTTP server. To activate this mode,
start it with

	pfg-server http

to use the default port number (41296), or give an explicit port number, e.g.,

	pgf-server http 8080

The HTTP server serves PGF files in the same way as the old FastCGI interface.
In addition, it also serves static files. The document root for static files
is the www subdirectory of the current directory where pgf-server is started.

In spite of these addition, backwards compatibility is maintaned. The old
FastCGI interface continues to work as before. (It is activated when
pgf-server is started without arguments.)

src/server/gf-server.cabal

@@ -16,6 +16,8 @@ executable pgf-server
                  gf >= 3.1,
                  cgi >= 3001.1.8.0,
                  fastcgi >= 3001.0.2.2,
+                 httpd-shed,
+                 network,
                  json >= 0.3.3,
                  utf8-string >= 0.3.1.1,
                  bytestring,
@@ -27,6 +29,8 @@ executable pgf-server
     FastCGIUtils
     Cache
     URLEncoding
+    RunHTTP
+    ServeStaticFile
   ghc-options: -threaded
   if os(windows)
     ghc-options: -optl-mwindows