[patch] depth handling in fill_table_cache broken when using select_related(depth=1).extra()

One-character patch plus one-line testcase

the description is slightly incorrect, because this bug happens also when not using extra(), for an example see #4789

Note: The patch in #4789 has a more extensive test case.

It also was already marked as ready before being prematurely closed as duplicate, which is why I am changing this ticket's state to "ready for check-in" now.

(In [6755]) queryset-refactor: Fixed an off-by-one error when filling the select-related case. Only affects people using select_related() with the "depth" parameter *and* extra(select=...) simultaneously. Refs #6018. Thanks, Matthias Urlichs.

(In [7477]) Merged the queryset-refactor branch into trunk.

This is a big internal change, but mostly backwards compatible with existing code. Also adds a couple of new features.

Fixed #245, #1050, #1656, #1801, #2076, #2091, #2150, #2253, #2306, #2400, #2430, #2482, #2496, #2676, #2737, #2874, #2902, #2939, #3037, #3141, #3288, #3440, #3592, #3739, #4088, #4260, #4289, #4306, #4358, #4464, #4510, #4858, #5012, #5020, #5261, #5295, #5321, #5324, #5325, #5555, #5707, #5796, #5817, #5987, #6018, #6074, #6088, #6154, #6177, #6180, #6203, #6658