FileUtils implementation broke compare_stream

FileUtils.compare_stream implementation in ruby 1.9.3 was doing something along the lines of

    a = b = nil

    while something

      a = as.read size

      b = bs.read size

      return false if a != b

    end

FileUtils.compare_stream in 2.0 instead does this:

    a = ""

    b = ""

    while something

      as.read size, a

      bs.read size, b

      return false if a != b

    end

which is a problem since default encoding for strings is UTF-8 and when File#read reads into UTF-8 string it remains UTF-8 but when StringIO#read reads into UTF-8 string it becomes encoding of StringIO source string, which is ASCII for FileBucket::File contents.

This leads to problems with backing up files and under certain conditions gives errors like:

Error: Could not back up /bin/whatever.pyc: Got passed new contents for sum {md5}ca60cf7b168557fb8c34be106b8c4ae8