getDirectoryContents blow its stack in a huge directory

Once a directory has around 2 million files in it, a lack of an accumulator in getDirectoryContents (unix version only; windows already has an acc) causes it to blow the stack:

joey@darkstar:‾/src/git-annex>cat test.hs
import System.Directory
main = do
	l <- getDirectoryContents "/tmp/big"
	print (null l)
joey@darkstar:‾/src/git-annex>ghc --make -O2 test
[1 of 1] Compiling Main             ( test.hs, test.o )
Linking test ...
joey@darkstar:‾/src/git-annex>./test
Stack space overflow: current size 8388608 bytes.
Use `+RTS -Ksize -RTS' to increase it.

I suggest the attached patch.

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/directory
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