tests/histedit-helpers.sh

branchmap: make branchcache responsible for reading

Encapsulate reading in a classmethod, to make it clear what kind of object is
being handled.

This is part of a stack of refactoring changes to help performance improvements
down the line.

Differential Revision: https://phab.mercurial-scm.org/D5635

fixbundle() {
    grep -v 'saving bundle' | grep -v 'saved backup' | \
        grep -v added | grep -v adding | \
        grep -v "unable to find 'e' for patching" | \
        grep -v "e: No such file or directory" | \
    cat
}