Use QLatin1Char when splitting on characters
Composer: Make sure to produce CRLF line endings when building messages

Looks like this has been compulsory at least since RFC2822 [1]. This means that
messages produced by Trojita for the last 9 months or so were not
standard-conforming :(. Sorry about that.

[1] http://tools.ietf.org/html/rfc2822#section-2.3