Merge branch 'bc/sequencer-export-work-tree-as-well'

"git rebase" started exporting GIT_DIR environment variable and exposing it to hook scripts when part of it got rewritten in C. Instead of matching the old scripted Porcelains' behaviour, compensate by also exporting GIT_WORK_TREE environment as well to lessen the damage. This can harm existing hooks that want to operate on different repository, but the current behaviour is already broken for them anyway. * bc/sequencer-export-work-tree-as-well: sequencer: pass absolute GIT_WORK_TREE to exec commands