Fixed #22531 -- Added `__repr__` for `tree.Node`

While Node class has a useful `__str__`, its `__repr__` is not that
useful. Added a `__repr__` that makes use of the current `__str__`.
This is especially useful since the more popular `Q` class inherits
`tree.Node`.
Merge branch 'q-objects-repr' of github.com:mmardini/django into q-objects-repr

Conflicts:
	django/utils/tree.py