maps: add the "branchmaxrevnum" method to RevMap Iterating the RevMap can be very expensive for large repos. To prevent future code from iterating the possibly huge RevMap causing performance issues, it's a good idea to clean all iterating code outside RevMap. This patch adds a method used by "get_parent_svn_branch_and_rev". In the future, we will have a SqliteRevMap, which will have an efficient implementation for this query, and it will disable "__iter__" to prevent future performance issues.

#!/bin/sh
. $(dirname $0)/common.sh

for b in `hg branches -aq` ; do
    hg co $b || break
    echo verifying $b
    hg svn verify
done