When the topic branch is deleted only the label is removed, commits
are stayed in the database, they are now merged into v2::
- o--o--o--o--o--M--< v2 - it is the mainline branch
+ o--o--o--o--o--M--< v2 - the mainline branch
\ /
- --*--*--* - it is the topic branch, now unnamed
+ --*--*--* - the topic branch, now unnamed
The topic branch is deleted to avoid cluttering branch namespace with
small topic branches. Information on what issue was fixed or what