cgm: fix creation of CGM Ellipse element ...

... which was breaking the loading of render-test.cgm and
tests/export/Ellipse.cgm with OpenOffice and probably other
CGM importers.

According to the specs the horizontal ellipse "endpoint" must come
first, the vertical second. Dia had it swapped since the beginning
of time.
pgf: Fix fill rule, alpha/transparency and optimize draw_beziergon

PGF is capablle to render bezier with holes and can do stroke and fill
in one step. ALso there is opacity for stroke and fill.
Included a small tex documented to test some of our sample diagrams with:
	pdflatex pgf-test