cmdutil: normalize log message eols when reading from file
This will be necessary once util.readfile() operates in binary mode. While
changelog.add() already normalizes the message, doing so in logmessage() is
required as ui.edit() or others expect messages with LF only.
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.