This allows deferring the XMapWindow call to after grabs succeeded, so
in case grabbing fails the screen no longer turns temporarily black.
This reduces the danger that someone may think grabbing succeeded then
closes their laptop.

Also, rename grab_window to background_window now that there's no longer
a grab on it.

It was a security hole due to suspend interaction. Let's rather not do
that, and instead provide the same feature via xss-lock's -n option.

Salvage the xss-lock supporting parts to instead inhibit suspends until
the screen is actually blanked - this prevents some information leaks.

Instead, let's do all with environment variables. It's more consistent
that way.

We require xss-lock's -l option to prevent sleep while unauthenticated
wakeup is allowed.

For extra paranoia, we're trying to detect xss-lock being the parent
process, and if so - and if its -l option is not used - we disable
unauthenticated wakeup.

Additional paranoia: arm not just a MONOTONIC but also a REALTIME timer, and forbid unauthenticated wakeup when either expires.

This prevents unlocking when the computer was sleeping while the timer was running.

Now shows like:

```
             Password:

            **********_
Keyboard: English (US), Caps Lock
```

Fixes #11.

This serves to provide a quick way to prevent the screen lock from
starting when accidentally launched (e.g. while watching a video).

The amount of time is controlled by the environment variable
XSECURELOCK_ALLOW_UNAUTHENTICATED_WAKEUP_TIME_SEC and can be set in the
range from 0 (feature turned off) to 10 (maximum allowed value).

During this time, the screen saver does not run and an animation
indicating this process is drawn instead.

Requires -lrt and CLOCK_MONOTONIC.

Fixes #12.

auth_pam_x11: support font selection

Usage:

- Find a good font name with xfontsel.
- Launch the screen saver via something like:

```
XSECURELOCK_FONT=-misc-fixed-medium-r-normal--20-200-75-75-c-100-iso10646-1 xsecurelock 
```

If the font can for some reason not be loaded, we're still falling back to fixed to allow SOME unlocking.

Many other screen savers send the wake-up keypress to the auth dialog,
so let's offer this feature to. Do read the security notes about this in
the source, though.

Fixes #14.

We have no need of handling this, however we don't want to spam about
this event on stderr.

Should fix some issues with semi-transparent notification windows.

It's sad that this is required, but some XScreenSaver hacks cause
XSecureLock to lose the grab on MotionNotify.

These can be overridden via:
- ./configure --with-default-auth-module=... --with-default-saver-module=...
- $XSECURELOCK_AUTH and $XSECURELOCK_SAVER environment variables
- Command line arguments (which work exactly as before)

Previously, the xset command sometimes got killed in response to
ScreenSaverNotify.

Instead, raise on VisibilityNotify. This makes sure possible email
notifications or other stuff show up as shortly as possible.

Quotes are required there...

Also, some minor changes done while auditing during documenting,
including fixes for:

- A file descriptor leak in the auth child (may DoS the screen).
- A race condition between querying display size and creating the
  window.