VERSION.txt, NEWS.txt: prepare version 6.7
Implement contour lines on terrain, closes #2451
Util/Macros: fix guard macro name
device: move overlap check to separate function
DeviceListDialog: make a few methods inline
device: use ExistsIf() in HaveCondorDevice()
device: pass DeviceConfig to devInitOne()
Merge branch 'v6.6.x'
Data/graphics: show version number 6.7
Makefile: remove gcc 4.5 workaround

We don't support gcc 4.5 anymore.
Makefile: simplify WERROR assignment
Makefile: move -Wuninitialized to warnings.mk
Makefile: enable -Wnested-externs on Android

Eliminates obsolete special case.
Topography/shapelib: don't redefine strlcpy() on Android

Bionic provides both strlcat() and strlcpy().  This allows us to
enable -Wredundant-decls.
Makefile: remove -Wuninitialized

This is implied by -Wall according to the gcc manual.
Makefile: move -O4 to debug.mk
Makefile: add dash to ARFLAGS

This is less ambiguous if the --plugin option was passed first.
Makefile: enable clang LTO only if LTO=y

Don't enable LTO via LLVM bitcode implicitly.
Thread/Posix{Mutex,Cond}: no constexpr on Android+clang

Works around clang error message:

 "non-literal type 'pthread_mutex_t' cannot be used in a constant
 expression"
Makefile: enable the Android "testing" flag

This is the unstable branch.