use cabal macro to detect if old version of network is being used

Utility/Url.hs

@@ -119,6 +119,11 @@ request url headers requesttype = go 5 url
 					Nothing -> return rsp
 					Just newURI -> go n newURI_abs
 						where
+#if defined VERSION_network
+#if ! MIN_VERSION_network(2,4,0)
+#define WITH_OLD_URI
+#endif
+#endif
 #ifdef WITH_OLD_URI
 							newURI_abs = fromMaybe newURI (newURI `relativeTo` u)
 #else

doc/bugs/network___62____61___2.4.0.1_is_not_in_Haskell_Platform_2012.4.0.0.mdwn

@@ -7,3 +7,6 @@ Do you think it's possible to support *both* versions of the network library, ma
 That would increase the portability of git-annex quite a bit.
 
 Thank you for your consideration.
+
+> Ok, I think I've figured out how to use the CPP macros defined by cabal
+> to deal with this. [[done]], will be in next release. --[[Joey]] 

git-annex.cabal

@@ -52,7 +52,7 @@ Flag DNS
 Executable git-annex
   Main-Is: git-annex.hs
   Build-Depends: MissingH, hslogger, directory, filepath,
-   unix, containers, utf8-string, network (>= 2.4.0.1), mtl,
+   unix, containers, utf8-string, network (>= 2.0), mtl,
    bytestring, old-locale, time,
    pcre-light, extensible-exceptions, dataenc, SHA, process, json, HTTP,
    base (>= 4.5 && < 4.7), monad-control, transformers-base, lifted-base,