Optimized background display, improves performance lost to my previous patch.

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6430 8aca7d54-2c30-db11-9de9-000461428c89
CODE: get rid of some unused height-scaling macros

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6431 8aca7d54-2c30-db11-9de9-000461428c89
Merge commit '8770d' into merge-from-standard
Merge commit '17c61' into merge-from-standard; required deletion of obsolete code in several other places

Conflicts:
	simconst.h
Fix serious error (introduced by James) in dataobj/einstellungen.cc regarding station_coverage_factories
Fix typo in previous fix.
Merge branch 'ncn-devel' into merge-from-standard
Fix further bug in factory coverage, affecting newly built factories
Merge branch 'ncn-devel' into merge-from-standard