[PATCH 0 of 1] Select internal conflict resolution tool with a merge option

[Isaac Jurado]

In order to achieve dummy merges, one has two options:

    hg --config ui.merge=internal:local merge
    hg debugsetparents . other_head

The first does not allow to define an alias of it due to the use of a global
option and the second does not performe the sanity checks included in merge
(like merging against ancestor).

The patch is just the idea and the proof of concept.  The name of the option and
the help text needs some love.  The merge command help string is intact at the
moment.