Relax the dm-crypt cipher regexp.
Deactive the block stack after use.
Stick to 4 spaces indent.
Keep the lens compatible with augeas 0.10.0.
Fix an inconsistency in extent editing.

This didn't show up in testing because it requires multiple segments.
Thankfully the inconsistency was caught by LVM.
We need Augeas 1.0.
Note kernel non-requirements.