That one was hairy... To summarize:
* We were setting Bone.head/tail (aka **local** rest location of bone) from EditBone data, using **EditBone's parent computed armature space**.
* We use those local head/tail to define Bone's restpose (in `BKE_armature_where_is_bone()`), using **Bone's parent armature space** (aka parent's arm_mat).
* Because of bone's roll nightmare, the two above parent's matrices will often not be the same.
In an ideal world, this should not affect locations (head/tail), but in real world of float it does - noticeably, in some extreme cases.
So! This commit cleans up things a bit (`fix_bonelist_roll()` was already doing much more than just fixing roll mess, has been renamed
to `armature_finalize_restpose()`), and ensures we do use (final!) parent's arm_mat local space to compute children's local head/tail as well.
This allows us to avoid too much imprecision here.
Checked the patch also with a complete Victor's rig from Gooseberry, seems to have no nasty side effects - fingers crossed!
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