svg: path codes 'q' and 't' debugged

Now the reference W3C_SVG_11_TestSuite/svg/paths-data-02-t.svg
is shown correctly (after some trial and error;))
svg: dia_svg_parse_path() vs TestSuite - path end handling

paths-data-18-f: unsupported path code '#'
=> all path-data-* passed visual inspection except for borked arcs
(paths-data-20-f.svg), which IMO is not worth the effort.
svg: improve matrix parsing and handling

 - basic support for makes the W3C test suite work better
 - don't let a non-invertible matrix screw cairo context,
   but just don't render with it as SVG expects it to be

animate-elem-34-t
  invalid matrix - by sequence of transforms: fixed.
coords-trans-08-t
  skewX skewY wrong transformation: fixed
coords-trans-09-t
  invalid matrix - by intent: matrix(0 0 0 0 0 0)
  stop cairo renderer complaints by not drawing
svg: tweak polyline creation

 - not only consider group's fill for closing, but also own attribute
 - don't crash on missing points attribute

painting-control-03-f
  close not only on group's fill, but also on self: fixed
svg: style tweaks

 - concatenate style string on multiple key definition
 - explain and change <use/> style use order
 - styling by <g/>
svg: use x,y from first <tspan/> as offset

Introduces _node_get_real() to simplify not only the new
parameter initialization but also all other applicable
places parsing positions and length.
svg: fix leak in _parse_shape_cp()
svg: line-join support for "Standard - Box"

of course not only for SVG
NEWS update
Bug 667509 - Translator Context for "Round"

Actually set for all Arrow, LineJoin, LineCap