tests/histedit-helpers.sh

tests: stabilize test-split.t for Windows

It looks like there will be additional problems beyond this trivial fix, but
this should make the bot green again.

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
}