Add "dumb" logging implementation to allow for writing unit tests.
Add piecewise_linear_tpl to abstract out the various piecewise-linear computations already present in experimental.
Revert "Add passengers discarded due to waiting too long to the "too slow" graph, not the "unhappy" graph (which represents overcrowding)"

This reverts commit ef4871750d5ae889a51756e9f2102338f8ad3695.
CHANGE: remove revenue penalty for travelling through overcrowded stations.
Improve comments
Minor improvements to piecewise_linear_tpl
Minor improvements in piecewise_linear_tpl.h
Change comments in piecewise_linear_tpl.h
Add architecture for linear interpolation for catering code.
Use inline conversion function in goods_frame_t.cc rather than specifying raw numbers.
Revise implementation of linear interpolation table for comfort to standardize units.
Switch all revenue computations to use new catering table...
FIX: gui tile dirty marking respect clipping rectangle

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6518 8aca7d54-2c30-db11-9de9-000461428c89
Merge branch 'ncn-devel' into mail-revenue
Use cached version of welt throughout gui/convoi_detail_t.cc
Remove another raw use of get_fare in favor of get_fare_with_speedbonus, and clean up errors in gui/convoi_detail_t.cc
Remove bogus file.
Unify (most of) refund computation to besch/ware_besch.cc.  Fix errors in booking refunds when avoid_overcrowding is active.
Remove (now) unused method from simware.h
Rework ai_goods.cc to use get_fare_with_speedbonus rather than get_fare.  The AI is still broken, though.