Revert "Removed OCE_DISABLE_TKSERVICE_FONT"

(This reverts commit a016096d4559bd601d96863f56f4afd4242c469c.)
Updated to work with latest version of OCE by adding a couple of
ifdef's in AIS/AIS_Dimension.cxx.

If the functions which require freetype are called, the implementation degrades nicely by using a fix-width overestimate of font with.