overflow2 is not exported by system libgd
Merge branch 'PHP-5.5'

* PHP-5.5:
  overflow2 is not exported by system libgd
temporary disable WBM detection with system libgd, as gdGetC, getmbi and skipheader not exported
Merge branch 'PHP-5.5'

* PHP-5.5:
  temporary disable WBM detection with system libgd, as gdGetC, getmbi and skipheader not exported