places plugin: remote-server gtk bookmarks not opened

In short, mintmenu won't open gtk bookmarks to remote systems if the bookmark has not already been mounted by gnome.

In detail...

Mint menu uses "xdg-open" to load any gtk bookmarks. This works fine for local bookmarks such as "file:///home/user/Documents", but doesn't work for gtk bookmarks pointing to remote systems, such as "sftp://user@server/". If the url has already been mounted by gnome as a network drive, xdg-open will work fine, but if the url has not been mounted, xdg-open (and the gnome command it calls, "gnome-open") will silently do nothing. (I'm betting this is a security feature, since xdg-open / gnome-open are used to load sometimes untrusted urls).

The only way I can see to fix this is to call "nautilus %s &" instead of "xdg-open %s &", since it has the correct behavior of auto-mounting remote bookmarks if needed. Other than that, it should behave in the exact same way as xdg-open.

Attached is a patch which uses nautilus instead of xdg-open for the gnome desktop only.