Manual en xc_tasks: Updated, auto waypoint "takeoff" included.
Manual en: Tiny typos and formulation.
Manual figuers: Reminder icon with a slicker round dot.
Manual en user interface: Aligning the menu button overviews.
Manual en atmosphere and instruments: More about weather forecasts.
Manual figures: Added last two missing gesture icons.
Manual en: Introduced new Config Plane dialogue / crossrefs in general menu overview partly corrected.
Manual en flash: Config Plane dialogue, Auto home wp, tiny fixes.
NEWS: prepare for 6.7.4
po: update French translation
IGCWriter: Fixed HFPLT header line

According to the current published specifications the long subtype should
be "PILOTINCHARGE" for the HFPLT header.
IGCWriter: Fixed HFDTM header line

According to the current published specifications the extended GPS datum
for code 100 should be "WGS-1984". (see example in section A9)
libpng: Fixed build errors

/usr/include/libpng12/png.h:2659:31: error: invalid suffix on literal; C++11 requires a space between literal and identifier [-Werror=literal-suffix]
        fprintf(PNG_DEBUG_FILE,"%s"m PNG_STRING_NEWLINE,(num_tabs==1 ? "\t" : \
                               ^

This seems to happen with newer versions of gcc. For example gcc 4.8.1-10
which is shipped as default with Ubuntu 13.10.
Merge branch 'v6.7.x'