reorder repo parameters last

Many functions took the repo as their first parameter. Changing it
consistently to be the last parameter allows doing some useful things with
currying, that reduce boilerplate.

In particular, g <- gitRepo is almost never needed now, instead
use inRepo to run an IO action in the repo, and fromRepo to get
a value from the repo.

This also provides more opportunities to use monadic and applicative
combinators.

Git/CatFile.hs

@@ -25,7 +25,7 @@ type CatFileHandle = (PipeHandle, Handle, Handle)
 {- Starts git cat-file running in batch mode in a repo and returns a handle. -}
 catFileStart :: Repo -> IO CatFileHandle
 catFileStart repo = hPipeBoth "git" $ toCommand $
-	Git.gitCommandLine repo [Param "cat-file", Param "--batch"]
+	Git.gitCommandLine [Param "cat-file", Param "--batch"] repo
 
 {- Stops git cat-file. -}
 catFileStop :: CatFileHandle -> IO ()