fix failure count memory leak

This is the last memory leak that prevents git-annex from running
in constant space, as far as I can see. I can now run git annex find
dummied up to repeatedly find the same file over and over, on millions
olf files, and memory stays entirely constant.

CmdLine.hs

@@ -80,7 +80,9 @@ tryRun' errnum state cmd (a:as) = do
 			a
 		handle (Left err) = showerr err >> cont False state
 		handle (Right (success, state')) = cont success state'
-		cont success s = tryRun' (if success then errnum else errnum + 1) s cmd as
+		cont success s = do
+			let errnum' = if success then errnum else errnum + 1
+			(tryRun' $! errnum') s cmd as
 		showerr err = Annex.eval state $ do
 			showErr err
 			showEndFail

doc/bugs/git_annex_add_memory_leak.mdwn

@@ -24,14 +24,9 @@ A history of the leaks:
   behind and could affect other git-annex commands. Fixed in versions afer
   3.20120123.
 
-* Something is still causing a slow leak when adding files.
-  I tested by adding many copies of the whole linux kernel
-  tree into the annex using the WORM backend, and once
-  it had added 1 million files, git-annex used ~100 mb of ram.
-  That's 100 bytes leaked per file on average .. roughly the
-  size of a filename? It's worth noting that `git add` uses more memory
-  than that in such a large tree.
-  **not fixed yet**
+* The count of the number of failed commands was updated lazily, which
+  caused a slow leak when running on a lot of files. Fixed in versions afer
+  3.20120123.
 
 * (Note that `git ls-files --others`, which is used to find files to add,
   also uses surpsisingly large amounts
@@ -40,3 +35,5 @@ A history of the leaks:
   before outputting anything.
   This is Not Our Problem, but I'm sure the git developers
   would appreciate a patch that fixes it.)
+
+[[done]]