created incorrect scale factors !!

    * src/autohint/ahglobal.c, src/autohint/ahglyph.c, src/autohint/ahhint.c:
    fixed the incorrect blue zone computations, and improved the composite
    support. Note that these changes result in improved rendering, while
    sometimes introducing their own artefacts. That's probably the last
    big change to the autohinter before the introduction of its complete
    replacement..