branchmap: use set for update code
We are doing membership test and substraction. new code is marginally faster.
$ hg init $ echo a > a $ hg add a $ hg commit -m testDo we ever miss a sub-second change?: $ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20; do > hg co -qC 0 > echo b > a > hg st > done M a M a M a M a M a M a M a M a M a M a M a M a M a M a M a M a M a M a M a M a