more cmdhelp revamp

more cmdhelp revamp

The if/elif/else/endif interpretor for '&' command data was too
simplistic.  It would allow multiple else clauses, elif clauses
after an else clause, and worst of all, accept a should-be-rejected
conditional block if an else or elif which evaluated true followed
an elif which evaluated false which in turn followed an earlier
true clause.  (dat/cmdhelp trigger any of those bugs.)