bittorrent: Fix mojibake introduced in parsing arai2c progress output.

hGetSomeString reads one byte at a time, so unicode bytes are not composed.
The problem comes when outputting that to the console with hPut; that
tried to apply the handle's encoding, and so we get mojibake.

Instead, use ByteStrings, and only convert it to a string for parsing, not
for display.

Note that there are a couple of other things that use hGetSomeString,
which I've left as-is for now.

debian/changelog

@@ -20,6 +20,7 @@ git-annex (5.20150206) UNRELEASED; urgency=medium
   * Improve race recovery code when committing to git-annex branch.
   * addurl: Avoid crash if quvi is not installed, when git-annex was
     built with process-1.2
+  * bittorrent: Fix mojibake introduced in parsing arai2c progress output.
 
  -- Joey Hess <id@joeyh.name>  Fri, 06 Feb 2015 13:57:08 -0400