absorb: preserve branch-closing changesets even if empty This makes the behavior consistent with 'hg commit', which allows to create otherwise empty changesets if they close the branch. A lost branch closure can inadvertently re-open a branch, so it should be preserved.

Greg Ward, author of the original bfiles extension
Na'Tosha Bard of Unity Technologies
Fog Creek Software
Special thanks to the University of Toronto and the UCOSP program