Dragging monitors in the display preferences left ghost images of the
previous position on systems without a compositor.

This patch removes creating an entire drawing context on the parent
window just for testing when edges touch and instead use a single-pixel
cairo surface. That way we avoid interfering with pending redraws. Then
we replace the manual canvas-to-window coordinate translation for
invalidation with a simple redraw call, which should handle windowless
widget positioning correctly.

Fixes #808

On illumos/Solaris, the passwd command requires a real terminal and
won't work over pipes. This adds a guarded code path so that the "Change
Password" dialog works on these platforms. The Linux/BSD behavior is
unchanged.

Fixes #384

Expose new titlebar mouse actions in the window properties
dialog (middle-click, right-click, scroll wheel).

Note: requires the matching marco changes to work properly.

This one was quite tricky ... On systems where pam_passwdqc
is installed the prompt for password after succesfully authenticating
is not:

```
New password:
```

But:

```
Enter new password:
```

See:

https://github.com/openwall/passwdqc/blob/7bf266fcf6ce9782b73722664e36dabd68f48c48/pam_passwdqc.c#L64

passwdqc is installed by default in Gentoo, but might be also installed
in other Linux distributions.