Fixup 920ba1f - make -help work again

We need to explicitly use pywikibot.argvu, or else two
copies of this array will be floating around (pywikibot.argvu
and pywikibot.bot.argvu). Setting it explicitly on pywikibot
makes sure the second one doesn't exist. Furthermore, make sure
the script name parser uses the working argvu.
Lastly, make the generic argument parser call pywikibot.argvu
instead of re-importing argvu locally.

Change-Id: I35ce3582bb74037d517a714d9d5f467d6b868bdb
Merge "Fixup 920ba1f - make -help work again"