Makefile: move XCSoar.exe rule to main.mk
Makefile: don't use $(OUTPUTS) for cab/dist

At this stage, $(OUTPUTS) hasn't been initalised completely, and the
rule may fail randomly.
Makefile: strip Kobo binaries

The Kobo has no self-hosting build environment; usually, one copies
stripped binaries to the Kobo.
Makefile: add rule to generate KoboRoot.tgz
Repetitive warning sound for airspace warnings dialog (enhancement #2952)

Adds repetitive warning sound when approaching or inside the prohibited airspace and
airspace warnings dialog is shown.
This is useful if you miss initial warning sound in sometimes noisy glider
cockpit and are close to airspace.
Warning sound is played with increased frequency as you are closer to airspace.
Enabling of this feature is configurable in Airspace configuration page by
checkbox "Repetitive Sound".
KoboMenu: eliminate attribute last_action

Return the action as the modal result code.
KoboMenu: use EXIT_SUCCESS and EXIT_FAILURE
KoboMenu: run XCSoar in a child process

Return to the menu after XCSoar has quit.
KoboMenu: use switch/case
KoboMenu: handle REBOOT, POWEROFF in main()
OS/FileUtil: use O_CLOEXEC in WriteExisting()
OS/FileUtil: add ReadString()
OS/FileMapping: use O_CLOEXEC
OS/FileUtil: add CreateExclusive()
kobo: add inittab and rcS

First steps towards a custom loader for XCSoar.
KoboMenu, rcS: reboot to launch Nickel

Due to a bug, Nickel fails to initialise the frame buffer properly,
therefore we need to reboot before launching the original Kobo
software.
Kobo: include Bitstream Vera fonts in KoboRoot.tgz
test/FakeLanguage: fix the #ifdef for Kobo/Android
Makefile: simplify ifeq/else chain
Makefile: remove Kobo library special cases

We don't need to specify the *.a files explicitly; using the "-l"
option is just as good.