Revert "auto merge of #2584 : pcwalton/servo/binary-search, r=SimonSapin...

..."

This reverts commit d8483d2365b234ec32478eb836fe6019bead9265, reversing
changes made to 3dedbd2719c78b636f4fd0860b07f1b53ed84c24.

Wikipedia crashes on linux after this change by attempting to index bogus glyphs.

This code is tricky enough that it's not obvious to me how to fix.