Fix stalls in S3 when transferring encrypted data.

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.

debian/changelog

@@ -3,6 +3,7 @@ git-annex (0.20110418) UNRELEASED; urgency=low
   * Don't run gpg in batch mode, so it can prompt for passphrase when
     there is no agent.
   * Add missing build dep on dataenc.
+  * Fix stalls in S3 when transferring encrypted data.
 
  -- Joey Hess <joeyh@debian.org>  Sun, 17 Apr 2011 14:29:49 -0400