Patch: Prompt for required password when mounting a drive

[Nate Nielsen <nielsen-list memberwebs com>]

When mounting a drive (listed in /etc/fstab) such as a an SMB, or
encrypted loop mount the 'mount' command will prompt for a password.
However when mounting that drive through gnome-vfs, there's nowhere for
the user to enter the required password.

This patch adds functionality to gnome-vfs so that when the 'mount'
command requests a password it prompts using a gnome-vfs-auth dialog.

Patch: http://bugzilla.gnome.org/attachment.cgi?id=50425
Bug: http://bugzilla.gnome.org/show_bug.cgi?id=157650

The 'mount' command prompts for passwords on /dev/tty. The patch opens a
tty and forks the 'mount' command with that as its stdin and stdout. It
then waits for a 'password:' string, etc...

This is a rough and incomplete patch, but I want to make sure this makes
sense and I haven't missed anything obvious.

Cheers,
Nate