bisect: use array.array rather than lists for ancestor lists
This nearly doubles performance and cuts memory usage in half on large
bisections.
adding src/a.c
moving src/a.c to source/a.c
1 files updated, 0 files merged, 1 files removed, 0 files unresolved
? src/a.o
merging src/a.c and source/a.c
1 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
M source/a.c
R src/a.c
? source/a.o