Mandate UTF-8 as file.encoding.

A better fix would avoid use of the platform default encoding
altogether.

Also adds a meta directive the the generated HTML to set the
encoding to UTF-8. We assume that the page that this is embedded
into follows the same conventions, either with a meta tag or with
a HTTP header.
Release notes for 2.11.0-M3

 - Correct Scala IDE section, after input from @dragos.
 - Improved the bug reporting section
 - Use the range v2.11.0-M1-v2.11.0-M3

Generated the commit list from the merge base of master and 2.10.x
and the soon-to-be-tagged 01dec25425@scala/scala.