Change log-tailer to properly track multi-byte characters.

When end-of-line is represented within a file as "\r\n",
it is represented in memory as a single "\n".  This patch eliminates
the discrepancy between size on disk and size in memory.
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

railties/lib/rails/rack/log_tailer.rb

@@ -24,7 +24,7 @@ def tail!
         if mod > @last_checked
           contents = @file.read
           @last_checked = mod
-          @cursor += contents.size
+          @cursor = @file.tell
           $stdout.print contents
         end
       end