winebrowser: Use user's preferred browser

[Jeremy White]

> +        "kfmclient exec,gnome-open,kmail,mozilla-thunderbird,thunderbird,evolution";

A Gnome user will be offended if you spool up the entire KDE environment
just to launch a URL; a KDE user will be similarly offended by gnome-open.
Further, if I'm a Gnome user, I may have KDE on my system, and kfmclient exec
may work, but it's likely to not be the browser I *really* want used.

The standard that's developing is that you don't invoke a KDE program
unless KDE_FULL_DESKTOP is set and you don't invoke a Gnome session
unless GNOME_DESKTOP_SESSION_ID is set.

Cheers,

Jeremy