[PATCH] Porrectus: third try

[Juergen Reuter]

Hi!

Attached is yet another patch for the porrectus engraver:

* Rewrote code for vaticana style porrectus grob; the solid shape is
  now drawn as a single bezier sandwich rather than composed from a
  couple of misused slurs.  Looks now much nicer.

* Added code to forbid line-breaking inbetween a porrectus
  (preliminary; to be moved to ligature engraver framework).

* Added auto-properties property for automatic determination of grob
  properties add-stem and stem-direction from musical context.

* Small clean-ups.

Greetings,
           Juergen

patch.diff
Description: Text document