tests/histedit-helpers.sh

errors: restructure formatparse() to clarify conditions a bit

The `similar` list will be calculated only for
`error.UnknownIdentifier`. It was then printed only if `inst.location
is None`, which is true for that exception type, but it's an indirect
condition to rely on.

Also, it looked from the code like it could both report similarities
and print a hint. That would be a little awkward because the
similarity report looks similar to the hint (both are printed within
parentheses). I also added a `elif` to clarify that. I plan to
refactor this more coming patches so the similarity report actually is
a hint.

Differential Revision: https://phab.mercurial-scm.org/D9343

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
}