LayoutEngine/Round: use 'roundf' instead of 'ceilf'

This removes wrong calculations for scrollbar's position
due to wrong rounding in Element's SetScrollLeft/Top
Merge pull request #156 from rndfax/master

LayoutEngine/Round: use 'roundf' instead of 'ceilf'
Merge branch 'master' into merge-test

* master:
  LayoutEngine/Round: use 'roundf' instead of 'ceilf'