Tracking dopesheet fixes:

- Dopesheet need to be updated when adding or switching
  between objects.
- After removing object it shall also be tagged for update,
  otherwise crash will likely happen.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55079 954f8c5b-7b00-dc11-b283-0030488c597c