TaskMacCreadyRemaining: call TaskPoint::GetType()

Change the reference variable from OrderedTaskPoint to TaskPoint.  Use
TaskPoint::GetType(), and cast to OrderedTaskPoint only after ensuring
that it's really an OrderedTaskPoint.  Not a real code change, just
cosmetic to make the cast less obscure.

This prepares for fixing assertion failure (#3186).
TaskMacCreadyRemaining: fix assertion failure on unordered task

This assertion was bogus.  get_aircraft_start() is legal for unordered
tasks, and it always had the proper checks.  Fixes TRAC #3186.  No
mention in NEWS because this was a debug-only crash.
ContestDijkstra: work around gcc 4.8 unordered_map bug

Due to an implicit copy of _Safe_sequence_base's linked list, the
destruction of a std::unordered_map copy invalidates all iterators of
the original object.  This commit changes the local copy to use the
assignment operator instead of the copy constructor.

See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59548 for the upstream
bug report.
Replay: fix skip to end-of-file after NMEA time warp

The Replay class was unable to recover from a time warp.
DeviceBlackboard: add local NMEAInfo reference variable
DeviceBlackboard: apply WrapClock after copying replay_data

See code comment.
Android/Product: declare "has_cursor_keys" on non-ARM

The "#ifdef __arm__" did not make sense for has_cursor_keys.  Fixes
build failure on ANDROID86 and ANDROIDMIPS.
test/TestWrapClock: increase accuracy requirements
Time/WrapClock: handle time warps with volatile input date

Split last_date into last_input_date and last_output_date.  Add
special checks for input dates that are not persistently adjusted
across Normalise() calls.

This fixes yet another midnight wraparound bug (TRAC #2973) which
occurred because the date adjusted by WrapClock::Normalise() was
overwritten by DeviceBlackboard::Merge().
test/TestWrapClock: additional tests with volatile input date

Unit tests for TRAC #2973.
Time/WrapTime: handle new GPS date without new GPS time on midnight

Yet another fix for TRAC #2973.
test/TestWrapClock: add test for "new date, old time"

Can happen on NMEAParser hiccup.
NMEA/Parser: move code to ::TimeHasAdvanced()
NMEA/Parser: check for midnight wraparound

TimeHasAdvanced() returns true when the time has just wrapped around.
This avoids discarding the first NMEA line after midnight.  The rest
will be fixed later by WrapClock.
po: update Slovak translation
po: update Russian translation
Form/TabDisplay: use alpha-blended tab icons on OpenGL

Our OpenGL port uses PNG images with an alpha channel instead of two
bit masks.
release v6.7.2
NEWS: prepare for 6.7.3
po: update Russian translation