kobo/rcS: create /dev/ttymxc1 and /dev/ttymxc2

For Kobo Touch, which was 3 on-board TTL port labeled J1, J2 and J3.
Terrain/RasterRenderer: cast to signed before division

Commit 212e15ff implicitly made the division "unsigned", which caused
a terrain rendering bug due to integer overflow (TRAC #3055).
Device/TTYEnumerator: search /sys/class/tty/

See code comment.
DeviceEditWidget: don't show the "/dev/" prefix
Form/List: no e-paper pixel panning in EnsureVisible()

This second check was missing, and could sometimes cause the
bottom-most item to be partly visible (TRAC #3043).
IO/CSVLine: std::copy() instead of strncpy()

strncpy() makes no sense here, because we don't need the null byte
check.  We already know the length.
Device/Parser: initialise BrokenDate::day_of_week

Make valgrind happy.
dlgTarget: remove obsolete OnDataAccess attributes

Missing piece of commit ae06f0b2.
InfoBoxes/Content: add "Takeoff Distance"

Implements TRAC #3059.
FlightStatisticsRenderer: fix indent
InfoBoxes/Contest: show average speed in OLC InfoBox (#2352)

Previously, the "comment" indicated the score, however that is
somewhat useless because the pilot already knows the distance.  The
average speed seems so much more interesting.
release v6.7_alpha2
Revert "InfoBoxes/Contest: show average speed in OLC InfoBox (#2352)"

This reverts commit 3a4cf581a73dc9e5b534e7d856511b1c0afd3670.

This commit removed display of the OLC score without decent alternative
breaking setup for existing users.
InfoBoxes/Content/Factory: Rename "OLC" infobox to "OLC Dist"
src/MapWindow/GlueMapWindowDisplayMode.cpp, src/Look/MapLook.?pp, src/Renderer/CompassRenderer.cpp, manual: Improvement of North arrow

The goals of this commit are
1/ to improve the graphical layout of the North arrow, now like conventionnal North arrow. now clearly different from other arrows used on map
2/ to improve its display logic. It now simply displays the North arrow as soon as circling or cruise is set to a different orientation than North up. The logic will not change current behavior for users chosing North up for both circling and cruise orientations (no North arrow).