Various changes and fixes for Log::Work

commit 5c2ca469f5cd3f1cbb2bca63254ee7d80c72e05c
make get_current_unit available during on_finish/on_error handlers

commit ad82dde653928384d7643732d84750c212bfa1ef
turn duration into rounded-off milliseconds instead of fractional seconds

commit b30ca69dcea836d7eab9d36d7dfbb7083ce40070
pretend we are not finished, so we can log errors and set results without additional errors

(Already merged in the stash changes)