Fix Vector.js rotate oversight in rP20263 (this.x may not be modified before reading again and sin/cos should not be computed twice).
Extend the tests of rotate in rP20262 to reveal the bug.
Add non-static clone functions for vectors (as the static ones were incorrectly removed in rP20125).
Math.pow performance is investigated separately, refs P85.

Checks and balances by mimo, leper, FeXoR and fatherbushido