Refactoring to use cabal-helper-wrapper

This turned out to be quite involved but save for this huge commit it's
actually quite awesome and squashes quite a few bugs and nasty
problems (hopefully). Most importantly we now have native cabal
component support without the user having to do anything to get it!

To do this we traverse imports starting from each component's
entrypoints (library modules or Main source file for executables) and
use this information to find which component's options each module will
build with. Under the assumption that these modules have to build with
every component they're used in we can now just pick one.

Quite a few internal assumptions have been invalidated by this
change. Most importantly the runGhcModT* family of cuntions now change
the current working directory to `cradleRootDir`.

Language/Haskell/GhcMod/Find.hs

@@ -28,7 +28,7 @@ import Language.Haskell.GhcMod.Utils
 import Language.Haskell.GhcMod.PathsAndFiles
 import Language.Haskell.GhcMod.Gap (listVisibleModules)
 import Name (getOccString)
-import Module (moduleNameString, moduleName)
+import Module (moduleName)
 import System.Directory (doesFileExist, getModificationTime)
 import System.FilePath ((</>), takeDirectory)
 import System.IO
@@ -81,7 +81,7 @@ loadSymbolDb :: IOish m => GhcModT m SymbolDb
 loadSymbolDb = do
     ghcMod <- liftIO ghcModExecutable
     tmpdir <- cradleTempDir <$> cradle
-    file <- chop <$> readProcess' ghcMod ["dumpsym", tmpdir]
+    file <- liftIO $ chop <$> readProcess ghcMod ["dumpsym", tmpdir] ""
     !db <- M.fromAscList . map conv . lines <$> liftIO (readFile file)
     return $ SymbolDb {
         table = db
@@ -102,12 +102,12 @@ loadSymbolDb = do
 --   The file name is printed.
 
 dumpSymbol :: IOish m => FilePath -> GhcModT m String
-dumpSymbol dir = do
+dumpSymbol dir = runGmPkgGhc $ do
     let cache = dir </> symbolCacheFile
         pkgdb = dir </> packageCache
 
     create <- liftIO $ cache `isOlderThan` pkgdb
-    when create $ (liftIO . writeSymbolCache cache) =<< getSymbolTable
+    when create $ (liftIO . writeSymbolCache cache) =<< getGlobalSymbolTable
     return $ unlines [cache]
 
 writeSymbolCache :: FilePath
@@ -127,9 +127,9 @@ isOlderThan cache file = do
         tFile <- getModificationTime file
         return $ tCache <= tFile -- including equal just in case
 
--- | Browsing all functions in all system/user modules.
-getSymbolTable :: IOish m => GhcModT m [(Symbol,[ModuleString])]
-getSymbolTable = do
+-- | Browsing all functions in all system modules.
+getGlobalSymbolTable :: LightGhc [(Symbol,[ModuleString])]
+getGlobalSymbolTable = do
     df  <- G.getSessionDynFlags
     let mods = listVisibleModules df
     moduleInfos <- mapM G.getModuleInfo mods