Merge and cherrypick outstanding 2.0 relevant patches from bzr.dev: Up to rev 4637, then 4639,4641,4643,4646,4649,4650,4651. (Robert Collins)
Log messages of the incorporated fixes:
revno: 4651 [merge] (robertc) Enable commit via record_iter_changes for specific file comments. (Robert Collins)
revno: 4650 [merge] Fix shelve on windows. (Robert Collins, #305006)
revno: 4649 [merge] (robertc) Make iter_changes produce output that is always safe to generate inventory deltas of in the same direction as the changes. (Robert Collins, #347649)
revno: 4646 [merge] (mbp) developer documentation about content filtering
revno: 4643 [merge] (mbp) small tweaks to release documentation
revno: 4641 [merge] (abentley) Shelve will not remove tree root.
revno: 4639 [merge] (andrew) Fix 'Revision ... not present' errors when upgrading stacked branches.
revno: 4637 [merge] Fix upgrade of branches in repositories.