branch: pass current transaction when writing branch in import

branch: pass current transaction when writing branch in backout command

branch: pass current transaction when writing branch in branch command

branch: pass current transaction when writing branch in merge

branch: pass current transaction when writing branch in rebase

branch: pass current transaction when writing branch in keyword

branch: pass current transaction when writing branch in histedit

dirstate: write the `branch` as part of the transaction if any Bypassing the transaction means we could get out of sync with the dirstatemap content. The branch is stil written right away if no transaction is around, but at least it no longer bypass the transaction. Actual caller of this still need to be updated.

dirstate: factor the transaction abort logic We will need it in more occasion if the branch is to be written as part of the transaction.

dirstate: use a context manager to handle the file used for writing the branch This is more modern.