GDI: Fixes mouse wheel scrolling bug on newer Windows versions.

For some odd reason under Win7 only downward scrolling was working. This
changes fixes it. Tested on Win2000 and Win7 systems.
Fixes a spelling mistake in a code comment.

Also removed trailing spaces from some lines.
aggpas: Makes the agg_2D.pas unit compilable again.
aggpas: New Agg2D Console demo.

See the unit's header comment for more details.