bundle2: mark the bundle2 part as advisory (issue5872)
It blocks old clients to read bundle including this part.
Differential Revision: https://phab.mercurial-scm.org/D3481
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
}