rebase: change "editform" to distinguish merge commits from others
"editform" argument for "getcommiteditor" is decided according to the
format below:
EXTENSION[.COMMAND][.ROUTE]
- EXTENSION: name of extension
- COMMAND: name of command, if there are two or more commands in EXTENSION
- ROUTE: name of route, if there are two or more routes in COMMAND
This patch newly adds "merge" as ROUTE, to distinguish merge commits
from other.
This patch passes bool as "ctxorbool" to "mergeeditform", because
working context has always 2 parents at this point. Dropping the
second parent of non-merging commits is executed in "concludenode".
Unlike other patches in this series (e.g. for "hg commit"), this patch
doesn't add "normal.normal"/"normal.merge" style ROUTEs, because there
is no "merge" case in "collapse" ROUTE.