Changed GeneratePow ensure xmm1 is loaded with y before making the test for N...

Changed GeneratePow ensure xmm1 is loaded with y before making the test for NaN

Committed: http://code.google.com/p/v8/source/detail?r=3966

[Rico, 2010-02-26 11:06:00]

Should handle the failures caused on win and mac - this was an error all along -
we actually bailed out to runtime way to often - so this has very positive
impact on performance.

[Lasse Reichstein, 2010-02-26 11:09:04]

LGTM