model: fixup happens_before/reflexivity, add 'curr' to lists earlier

model: fixup happens_before/reflexivity, add 'curr' to lists earlier

Some code under 'check_current_action' assumes that the current action is not
added to the ModelChecker trace/list data structures yet. However, some
features I need to add will require the current action to be in these
data structures already. So there are a few spots I need to fixup so that the
code can handle "happens_before" reflexivity properly.

This commit moves the "add_action_to_lists()" call as well as fixes up
reflexivity.