mail/msmtp: fix configuration for gnome password management

In order to enable password management, now '--with-libsecret'
option should be used instead of '--with-gnome-keyring'.

So fix configure args and rename the GNOMEKEYRING option to
LIBSECRET.

Also modernize options usage and bump PORTREVISION due to
package change.

PR: 204760 (with minor edits)
Submitted by: John Hein
MFH: 2015Q4