tests/histedit-helpers.sh

revlogdeltas: always return a delta info object in finddeltainfo

Previously, the method returned `None` when a full snapshot was needed. The
caller had to determine how to produce one itself.

In practice, building a `_deltainfo` object for a full snapshot is simple. So
we build it at the `finddeltainfo` level and always return a `_deltainfo`
object.

The caller can now simply process the `_deltainfo` return in all cases.

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
}