VERSION: Increment to 11.15 development build
Merge branch 'master' into 11.x

Conflicts:
	simversion.h
FIX: Set the default minimum runway length for paksets not compatible with the minimum runway length feature to 10m rather than to 0m, as a length of 0m implies VTOL.
FIX: Power stations in cities acted as consumers of electricity as well as producers.
FIX: Skip multiple substation distribution code where there is only one substation in a city.
CHANGE: Upgrade dr_rdpng.cc to the latest version from standard.
CHANGE: Increase the default rolling resistance of tramways and roads according to historical research
FIX: Makeobj project files were not configured correctly
FIX: Maximum speed and weight were not displayed in the tooltip for ways with prohibitive way constraints
FIX: Crash on reversing in some cases
CHANGE: Further increase of default rolling resistance for trams (4x that of rail)
FIX: Errors in calculating routes with long-block signals and, in some cases, choose signals
FIX: Crash in some cases relating to tram elevated ways
FIX: Crashes after map expansion in some cases.
FIX: Passengers and cargo would sometimes go missing when loading
VERSION: Step to release build