In anticipation of importing more test suites.

This test font had a upem of 769, which results in rounding-related errors with
the FreeType font funcs.  Change the upem to 1024 to fix that.

Fixes https://github.com/behdad/harfbuzz/issues/201

We use three bits for lig_id these days, so we finally got a report of
two separate ligatures with the same lig_id happening adjacent to each
other, and then the component-handling code was breaking things.
Protect against that by ignoring same-lig-id but lig-comp=0 glyphs after
a new ligature.

Fixes https://github.com/behdad/harfbuzz/issues/198