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
git-svn-id: https://svn.wildfiregames.com/public/ps/trunk@20272 3db68df2-c116-0410-a063-a993310a9797