The variable force_highlight_callback is gone. Highlight functions are now consistently named SyntaxCheckers_<filetype>_<checker>_GetHighlightRegex(), and they take precedence over highlighting based on column.
This can be done with: `let g:syntastic_mode_map={'passive_filetypes': 'vala'}` or by setting `let g:syntastic_vala_checkers=[]` Closes #502.