Use the PROVIDES mechanism so that msmtp and msmtp-nossl can be be
+depended-on and avoid generating a file level conflict. Also use
alternatives for msmtp-mta and msmtpq-ng-mta with msmtp-mta since
we can only have one sendmail at a time.
Signed-off-by: Daniel F. Dickinson <cshored@thecshore.com>