Comment threading depth of "1" disabled threading and is redundant and confusing

[markjaquith]

When comment threading is enabled and the depth is set to 1, threading will not work, because the depth is total depth, not depth of child comments.

There is a checkbox to enable/disable threading, so it is confusing and redundant to allow setting depth to 1. My WordPress.com blog has sat like that for 8 months and I thought it wasn't working because the theme didn't support it!

The depth should start at 2. That also has the benefit of making obvious that it's talking about total depth, instead of depth of child comments.

[markjaquith]

(In [11958]) Eliminate the redundant and confusing comment threading depth of 1. Threading starts at 2 now. fixes #10829