Removed support for git versions older than 2.1

debian oldoldstable has 2.1, and that's what i386ancient uses. It would be
better to require git 2.2, which is needed to use adjusted branches, but
can't do that w/o losing support for some old linux kernels or a
complicated git backport.

Git/CheckIgnore.hs

@@ -15,7 +15,6 @@ module Git.CheckIgnore (
 import Common
 import Git
 import Git.Command
-import qualified Git.Version
 import qualified Utility.CoProcess as CoProcess
 
 import System.IO.Error
@@ -29,17 +28,11 @@ type CheckIgnoreHandle = CoProcess.CoProcessHandle
  - GIT_FLUSH behavior flushing the output buffer when git check-ignore
  - is piping to us.
  -
- - The first version of git to support what we need is 1.8.4.
- - Nothing is returned if an older git is installed.
- -
  - check-ignore does not support --literal-pathspecs, so remove that
  - from the gitGlobalOpts if set.
  -}
-checkIgnoreStart :: Repo -> IO (Maybe CheckIgnoreHandle)
-checkIgnoreStart repo = ifM supportedGitVersion
-	( Just <$> gitCoProcessStart True params repo'
-	, return Nothing
-	)
+checkIgnoreStart :: Repo -> IO CheckIgnoreHandle
+checkIgnoreStart repo = gitCoProcessStart True params repo'
   where
 	params =
 		[ Param "check-ignore" 
@@ -52,11 +45,6 @@ checkIgnoreStart repo = ifM supportedGitVersion
 	pathspecs (Param "--literal-pathspecs") = True
 	pathspecs _ = False
 
-supportedGitVersion :: IO Bool
-supportedGitVersion = do
-	v <- Git.Version.installed
-	return $ v >= Git.Version.normalize "1.8.4"
-
 {- For some reason, check-ignore --batch always exits nonzero, 
  - so ignore any error. -}
 checkIgnoreStop :: CheckIgnoreHandle -> IO ()