Makefile: add variable "TARGET_IS_ARM"
Makefile: add option "GLES"

Use OpenGL/ES on by default on all ARM devices, including the
Cubieboard.
Makefile: disable GLES on Cubieboard for now

This requires some more glue code to combine SDL with GLES.  Later.
release v6.6
android.mk: Simplified NATIVE_HEADERS dependencies
android.mk: Pass cache setting to submakes
NEWS: prepare for 6.6.1
VERSION.txt, NEWS.txt: prepare version 6.7
Implement contour lines on terrain, closes #2451
Makefile: link harness.a with src/Audio/VegaVoiceSettings.cpp

Fixes linker failures.
po: update Polish translation
po: update German translation
po: update xcsoar.pot
Util/Macros: fix guard macro name
device: move overlap check to separate function
DeviceListDialog: make a few methods inline
device: use ExistsIf() in HaveCondorDevice()
DeviceListDialog: indicate duplicate devices in list

Label them "duplicate" instead of "error".
device: compare port type first in DeviceConfigOverlaps()

Simplifies the function by reducing duplicate code.  The PortType::PTY
case was broken because the type comparison was hard-coded to
PortType::SERIAL.
device: allow using more than one TCP/UDP device

Compare the configured port in DeviceConfigOverlaps().  Now two TCP
devices don't overlap if the port is different.