Use align-grob in define-grobs.scm: AccidentalSuggestion

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Use align-grob in define-grobs.scm: AmbitusLine

TODO: Apparently there is something wrong with AmbitusLine,
because a warning "AmbitusLine has empty extent and non-empty
stencil" pops out.  Obviously, AmbitusLine's stencil isn't
empty, because there's a line to be printed.  It seems that
LilyPond fails to set appropriate extent, which should be
automatically calculated from the stencil.

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Use align-grob in define-grobs.scm: GridLine

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Use align-grob in define-grobs.scm: MultiMeasureRest stuff

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Use align-grob in define-grobs.scm: OctavateEight

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Use align-grob in define-grobs.scm: PercentRepeatCounter

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Use align-grob in define-grobs.scm: Script

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Use align-grob in define-grobs.scm: StemTremolo

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Remove centered_on_._parent from Self_alignment_interface.

These functions were replaced with align_grob and are now
obsolete.

TODO: write convert-ly rule.
Use align-grob in define-grobs.scm: BarNumber

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Use align-grob in define-grobs.scm: CombineTextScript

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Use align-grob in define-grobs.scm: InstrumentName

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Use align-grob in define-grobs.scm: InstrumentSwitch

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Use align-grob in define-grobs.scm: MetronomeMark

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Use align-grob in define-grobs.scm: RehearsalMark

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Use align-grob in define-grobs.scm: pedals

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Use align-grob in define-grobs.scm: TabNoteHead

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Use align-grob in define-grobs.scm: TextScript

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Use align-grob in define-grobs.scm: Flag

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allow to use nonstandard extents for alignment