filter-branch: skip commits present on --state-branch

filter-branch: skip commits present on --state-branch

The commits in state:filter.map have already been processed, so don't
filter them again. This makes incremental git filter-branch much faster.

Also add tests for --state-branch option.

Signed-off-by: Michael Barabanov <redacted>
Acked-by: Ian Campbell <redacted>
Signed-off-by: Junio C Hamano <redacted>