Fix floating/exploding dynamic physicals

Only put dynamics to sleep if they're at the initial location. This
prevents baskets from exploding on touch by an avatar and should
theoretically make the doggone slave cave kickables activate the pressure
plates.
Fix plStringBuffer constructor with explicit size to count chars, not bytes
Merge pull request #436 from zrax/plStringBuffer_sizeof

Fix plStringBuffer constructor with explicit size to count chars, not bytes
Merge pull request #419 from Hoikas/physx_sleep

Fix long-standing physical sleep issue.