Fix ticket 312 - TimeToDie not working.

Timespan computations were not working when the start a time interval was
infinity (math.huge).  Clamp the time to die to be a very large number
instead of infinity so that (start, math.huge) is still a valid timespan.

git-svn-id: svn+ssh://svn.curseforge.net/wow/ovale/mainline/trunk@1125 d5049fe3-3747-40f7-a4b5-f36d6801af5f