- merged path_based_options branch

- merged path_based_options branch
- behavior of query.options() is now fully based on paths, i.e. an option
  such as eagerload_all('x.y.z.y.x') will apply eagerloading to only
  those paths, i.e. and not 'x.y.x'; eagerload('children.children') applies
  only to exactly two-levels deep, etc. [ticket:777]
- removes old compiler()/schemagenerator()/schemadropper() methods from mysql dialect