In Orberg’s LLPSI he has: Ariadna amicum suum fugientem vocavit: “Theseu! Theseu! Revertere ad me!”
I take it that ‘revertere!’ here is passive imperative and means something like ‘be returned to me’. I’m not clear of the difference in use between the passive and active in this verb.
Edit: What Adrianus said. 
“Revertor” verbum et deponens est, ergo "anglicè “Return!” est “Revertere!”
“Revertor” is also a deponent verb, so “Revertere!” means also “Return!”
Salve Alati!
So the table in 501 Latin Verbs showing ‘active’ and ‘passvive’ forms are really showing two columns that mean exactly the same thing…???
No, a passive imperative doesn’t mean the same thing as an active. It’s just that the imperative of a deponent verb is going to be passive in form but active in meaning, just like virtually everything else about deponent verbs (participles aside).
I believe passive imperatives are pretty rare outside of deponent verbs, though. A passive command for an active verb can be rephrased such that the passive imperative is not needed. Besides, how often have you needed a passive imperative in English? “Be carried on his shoulders!” is more awkward than “Let him carry you on his shoulders!” (“Tē umerīs ferat”), isn’t it?
Often when you want to be abusive! And often with negative orders.
Saepè anglicè taliâ voce modo imperativo uteris contumeliosé! Saepè et cum jussu negativo.
Yes but if ‘Revertor" is also a deponent verb, so “Revertere!” means also "Return!’‘’ then what is the difference in meening between the active and passive forms of this verb?
None (almost), unless that between “Go!” and “Be gone!” or, more appropriately here, “Back!” and “Get back!” in English. Check the dictionary for some small differences depending on context.
Nulla (paenè) differentia, nisi ea inter anglicè “Go!” et “Be gone!” vel hîc aptiùs “Back!” et “Get back!” In dictionarium humiles inquire de contextu pendentes.
Do deponent verbs even have active imperatives? 
Wheelock – though it is not an exhaustive reference – only lists the passive imperative forms for deponent verbs.
No (if you’re not referring to the active sense of the passive voice). But pmda means the anomalous situation of “reverte” from “reverto” as a non-deponent and “revertere” from “revertor” as a deponent.
Non habent (at certè sensum activum è voce passivâ surgit). Pmda autem formas deponentem (de “revertor”) et non deponentem (de “reverto”) ut anomalias distinguit.
Ah. I hadn’t come across that before.