compiler: replace MODESWTICH POINTERARITHMETICS with $POINTERMATH directive, disable pointer arithmetic in delphi mode by default (compatible with delphi), enable pointer arithmetic in fpc/objfpc modes as they had it enabled by default before, add has_pointer_math field to tpointerdef to allow pointer arithmetic with such pointer even if pointer math mode is off (delphi compatible) + tests

git-svn-id: trunk@16651 -