tests/histedit-helpers.sh

rebase: use hard-coded template for one-line commit description

This is to prepare for making making the one-line summary
customizable. The template ended up pretty complicated because of the
conditional output of "(<bookmarks etc>)". Maybe we can simplify the
template later.

Differential Revision: https://phab.mercurial-scm.org/D9250

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
}