version: workaround build failure on Cabal-1.14

Cabal-1.14 does not generate VERSION_pronk symbol in cabal_macros.h.
Likely a Cabal bug, but we can use base's facility to get the same.

    # ./Setup.lhs build
    [1 of 1] Compiling Main             ( app/App.hs, dist/build/pronk/pronk-tmp/Main.o )
    app/App.hs:88:41: Not in scope: data constructor `VERSION_pronk'

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

app/App.hs

@@ -1,4 +1,4 @@
-{-# LANGUAGE BangPatterns, CPP, DeriveDataTypeable, OverloadedStrings,
+{-# LANGUAGE BangPatterns, DeriveDataTypeable, OverloadedStrings,
     RecordWildCards, ScopedTypeVariables #-}
 
 module Main (main) where
@@ -14,11 +14,13 @@ import Data.Text (Text, pack)
 import Data.Text.Encoding (encodeUtf8)
 import Data.Text.Lazy.Builder (toLazyText)
 import Data.Time.Clock.POSIX (getPOSIXTime)
+import Data.Version (showVersion)
 import Network.HTTP.LoadTest (NetworkError(..), Req(..))
 import Network.HTTP.LoadTest.Analysis (analyseBasic, analyseFull)
 import Network.HTTP.LoadTest.Environment (environment)
 import Network.HTTP.LoadTest.Report
 import Network.Socket (withSocketsDo)
+import Paths_pronk (version)
 import Prelude hiding (catch)
 import System.CPUTime (getCPUTime)
 import System.Console.CmdArgs
@@ -50,6 +52,9 @@ data Args = Args {
     , json :: Maybe FilePath
     } deriving (Eq, Show, Typeable, Data)
 
+pronk_version :: String
+pronk_version = showVersion version
+
 defaultArgs :: Args
 defaultArgs = Args {
                 concurrency = 1
@@ -85,7 +90,7 @@ defaultArgs = Args {
               , json = def &= typ "FILE"
                 &= help "Save analysis in JSON format"
               } &= verbosity
-                &= summary ("Pronk " ++ VERSION_pronk ++
+                &= summary ("Pronk " ++ pronk_version ++
                             " - a modern HTTP load tester")
 
 fromArgs :: Args -> E.Request IO -> LoadTest.Config