merge: use constants for actions We finish up establishing named constants in this file with actions. I remember scratching my head trying to figure out what this code was doing as part of addressing a recent security issue with subrepos. Having the named constants in place definitely makes things easier to read. I'm not convinced the new constants have the best names (I'm not an expert in this code). But they can be changed easily enough. Also, since these constants are internal only, we might want to change their values to something more human readable to facilitate debugging. Or maybe we could employ an enum type some day... Differential Revision: https://phab.mercurial-scm.org/D2701

running: init test1
result: None
running: add foo
result: 0
running: commit -m commit1 -d 2000-01-01 foo
result: None
running: commit -m commit2 -d 2000-01-02 foo
result: None
running: log -r 0
changeset:   0:0e4634943879
user:        test
date:        Sat Jan 01 00:00:00 2000 +0000
summary:     commit1

result: None
running: log -r tip
changeset:   1:45589e459b2e
tag:         tip
user:        test
date:        Sun Jan 02 00:00:00 2000 +0000
summary:     commit2

result: None