[PATCH 0 of 2 STABLE V3] histedit: abort if there are multiple roots in "--outgoing" revisions

[FUJIWARA Katsunori]

This patch series makes "histedit --outgoing" aborts if there are
multiple roots in "--outgoing" revisions.

Difference between V2 and V3:

  - split a patch into one to fix and another to add help document,
    for separate discussion

  - disuse term "root"/"roots" in abort message and help document for
    novice users