Quoting glibc rand(3):

The  versions  of rand() and srand() in the Linux C Library use the same random
number generator as random(3) and srandom(3), so the lower-order bits should be
as  random  as  the  higher-order bits.   However,  on  older  rand()
implementations, and on current implementations on different systems, the
lower-order bits are much less random than the higher-order bits.  Do not use
this function in applications intended to be portable when good randomness is
needed.  (Use random(3) instead.)

Trying to handle stdin when select() in fact returned an error due to being
interrupted by a signal is a rather bad idea.

See issue #405

Fixes non-random behaviour when randomizing file lists several times per
second.

Closes #349

Happens e.g. when using -O without enabling thumbnail/index mode

Closes #335

When feh loses its controlling terminal at runtime, e.g. due to backgrounding /
disowning, it will no longer issue a warning on each terminal keystroke.

As there's no "default" window, it doesn't make much sense here...
Plus, it's buggy as hell in this mode

Also, restore the previous terminal mode on exit

Problems so far:
* leaks zombie processes
* does not work when terminating feh with a signal (since the convert process
  is no longer in feh's process group)

Squashed commit of the following:

commit 55e66e15af898f4c01d7d265013124fefce795e4
Author: Daniel Friesel <derf@finalrewind.org>
Date:   Mon Sep 26 19:59:46 2011 +0200

    Save all filenames in ~/.fehbg

commit afc2774f315fc379aa96de58decf8370772036af
Author: Daniel Friesel <derf@finalrewind.org>
Date:   Mon Sep 26 19:24:38 2011 +0200

    Update test/bg --bg-fill images (off-by-one due to changed implementation)

commit bd4210cff2e895414df12868f6cab7f193c5adf5
Author: Daniel Friesel <derf@finalrewind.org>
Date:   Mon Sep 26 14:47:00 2011 +0200

    Fix feh_wm_set_bg_maxed

commit d9ada9dc2a74aef6ae0924e9c0ff296b94ee25bc
Author: Daniel Friesel <derf@finalrewind.org>
Date:   Mon Sep 26 14:39:11 2011 +0200

    Fix for non-xinerama setups

commit be2cf0f1f8c00b737e7141a372d3cbc9db4c949f
Author: Daniel Friesel <derf@finalrewind.org>
Date:   Mon Sep 26 14:24:44 2011 +0200

    Move wallpaper calculation code into separate functions

commit 4e07c1f9734569fdd778a813c5a85c63b51b3175
Author: Daniel Friesel <derf@finalrewind.org>
Date:   Mon Sep 26 13:01:46 2011 +0200

    Remove unnecessary temporary variable

commit 23d1d733b21d1560e1fbcadddc34cae3d666b21d
Author: Daniel Friesel <derf@finalrewind.org>
Date:   Mon Sep 26 12:46:25 2011 +0200

    Initial conversion, works with --bg-scale

feh -O should also be able to run without it, but that requires slightly more work.
I'll fix that one later, I guess.

<http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=373209>