Add acciaccatura (crossed grace notes) rendering for <graceGrp>

[FrithjofVollmer]

Would it be conceivable to add the acciaccatura (crossed grace note) rendering of @grace="unacc" to <graceGrp> as well? (works already when attributed to <note>)

[FrithjofVollmer]

Code sample: doesn't work with

<graceGrp grace="unacc">
    <note dur="8" oct="2" pname="a" stem.dir="up" />
    <note dur="8" oct="2" pname="b" stem.dir="up" />
</graceGrp>
<note dur="2" oct="3" pname="f" />                       

yet, but it does work with

<note dur="8" oct="2" pname="a" grace="unacc" stem.dir="up" />
<note dur="2" oct="3" pname="f" />            

[lpugin]

The code sample needs to b e a minimal but processable example.