evolve: remove meaningless transaction nesting Before this patch, functions below nest transaction scope, even though they are invoked only inside a transaction scope created at _solveone(). - _solvebumped() - _solvedivergent() - relocate() via _solveunstable() or _solvebumped() Transaction nesting is useful for localizing "success" (e.g. one scope per commit inside wider scope for multiple committing). But such nesting is redundant for _solveone(), because there is no code path, which causes failure after successfully closing inner transaction(s). In addition to it, this nesting makes it complicated to close current transaction successfully with exception raising inside inner scope, like "hg shelve" at detection of conflicts. "tr.close()" is required at each outer scopes for such case. To remove meaningless transaction nesting, this patch replaces repo.transaction() in functions above by repo.currenttransaction(). This reuses transaction created at _solveone(). This patch also adds 'assert tr' after getting current running transaction, to avoid invocation of functions above without transaction.