The current OpenType Feature File specification is silent about
what the proper behavior should be when a single glyph has multiple
LigatureCaretByPos or LigatureCaretByIndex statements. After
this change, we match the behavior of Adobe's `makeotf` tool.
Arguably, `makeotf` might not be optimal in its current behavior,
but it seems better to match the existing toolchain than to have
two conflicting interpretations of an ambiguous spec. Once the
specification gets clarified, we will of course follow.
See https://github.com/adobe-type-tools/afdko/issues/95 for the
spec discussion.
