grace note cancels \voiceOne etc

[Arvid Grøtting]

>> [This line intentionally not left quite blank]

As of 2.11.17, any kind of grace note cancels \voiceOne etc. from that point
onwards, even across voices or (not shown here) staffs.

This works fine in 2.10, and I think it worked in 2.11.5 as well.  It definitely
failed in 2.11.16; haven't tried any more in-between versions.

\version "2.11.17"

\score {
  \context Score <<
    \new Staff <<
      \new Voice {
        \relative c'' { 
          \voiceOne
          c4 e g c c g e c \bar "||"
          \grace d8 c4 e g c c g e c \bar "||"
        }         
      }
      \new Voice {
        \relative c' {
          \voiceTwo
          \repeat unfold 4 { c4 d e d }
        }
      }
    >>
  >>
  \layout {}
}