Another fix for buff conditions.

Another fix for buff conditions.

Back out r1321 and partially re-implement r1252 by giving the results of
those conditions a time span that starts when the buff starts and lasting
to infinity.

This fixes uses of buff conditions for buffs that are applied in the
future, e.g., a spell applies a DoT at end of spellcast and something
like:

    if target.DebuffRemains(dot) < 3 Spell(spell_that_applies_dot)

git-svn-id: svn://svn.curseforge.net/wow/ovale/mainline/trunk@1337 d5049fe3-3747-40f7-a4b5-f36d6801af5f