Since hS3 needs Crypto anyway, this actually reduces dependencies.

The remaining leaks are in hS3. The leak with encryption was worked around
by the use of the temp file. (And was probably originally caused by
gpgCipherHandle sparking a thread which kept a reference to the start
of the byte string.)

Provide file size to new version of hS3.

* Update Debian build dependencies for ghc 7.
* Debian package is now built with S3 support. Thanks Joachim Breitner for
  making this possible, also thanks Greg Heartsfield for working to improve
  the hS3 library for git-annex.

Also hid a conflicting new symbol from Control.Monad.State

Finished applying to S3 the change that fixed the memory leak in bup, but
it didn't seem to help S3.. with encryption it still grows to 2x file size.

This was a most surprising leak. It occurred in the process that is forked
off to feed data to gpg. That process was passed a lazy ByteString of
input, and ghc seemed to not GC the ByteString as it was lazily read
and consumed, so memory slowly leaked as the file was read and passed
through gpg to bup.

To fix it, I simply changed the feeder to take an IO action that returns
the lazy bytestring, and fed the result directly to hPut.

AFAICS, this should change nothing WRT buffering. But somehow it makes
ghc's GC do the right thing. Probably I triggered some weakness in ghc's
GC (version 6.12.1).

(Note that S3 still has this leak, and others too. Fixing it will involve
another dance with the type system.)

Update: One theory I have is that this has something to do with
the forking of the feeder process. Perhaps, when the ByteString
is produced before the fork, ghc decides it need to hold a pointer
to the start of it, for some reason -- maybe it doesn't realize that
it is only used in the forked process.

Stalls were caused by code that did approximatly:

content' <- liftIO $ withEncryptedContent cipher content return
store content'

The return evaluated without actually reading content from S3,
and so the cleanup code began waiting on gpg to exit before
gpg could send all its data.

Fixing it involved moving the `store` type action into the IO monad:

liftIO $ withEncryptedContent cipher content store

Which was a bit of a pain to do, thank you type system, but
avoids the problem as now the whole content is consumed, and
stored, before cleanup.

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