merge: introduce tool.check parameter
tool.check is a list of check options, and can be used in place of
tool.checkchanged and tool.checkconflicts:
Equivalences:
tool.checkchanged = yes
tool.checkconflicts = no
tool.check = changed
tool.checkchanged = no
tool.checkconflicts = yes
tool.check = conflicts
tool.checkchanged = yes
tool.checkconflicts = yes
tool.check = changed, conflicts
Add _toollist() wrapper for ui.configlist() to implement this consistently.
checkchanged and checkconflicts are still supported, but check is
preferred for implementing new check options.