Fix arguments to GetDuration() (it only takes 3 arguments).

Also guard against zero tick lengths (shouldn't happen but you never know)
and add some comments to clarify what's happening in the code.

git-svn-id: svn+ssh://svn.curseforge.net/wow/ovale/mainline/trunk@846 d5049fe3-3747-40f7-a4b5-f36d6801af5f
Also return number of ticks from OvaleData:GetDuration().

It already computed the information, so return it as well so the caller
doesn't have to make that same error-prone floating-point computation.

git-svn-id: svn+ssh://svn.curseforge.net/wow/ovale/mainline/trunk@847 d5049fe3-3747-40f7-a4b5-f36d6801af5f
Fix two bugs in OvaleBestAction.

(1) Missed a variable rename that caused channeled spells to trigger Lua
    error, broken in commit r843.  This fixes ticket #226.

(2) Spell priorities were broken in commit r816.

Also improve some of the comments in this file to better document what's
happening.

git-svn-id: svn+ssh://svn.curseforge.net/wow/ovale/mainline/trunk@848 d5049fe3-3747-40f7-a4b5-f36d6801af5f