histedt: use inheritance to override the constraints in 'base'
All actions but one actually have the same constraints when it comes to validate
the 'action.node' value. So we actually just add this code to a method that can
be overwritten in the one action where it matters.
The now unused 'contraints' related enum and class attribute will be cleaned up
in the next changeset.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.