tests/histedit-helpers.sh

errors: move Abort earlier, so more exceptions can subclass it

I'd like to make at least `InterventionRequired` subclass `Abort` and
Python requires the superclass to be defined before the subtype.

Differential Revision: https://phab.mercurial-scm.org/D10736

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
}