X64 Crankshaft: Implement MathRound, MathFloor, MathSqrt, and MathPowHalf UnaryMathOperations in optimizing code generator.  Remove unneeded bailout on Math.pow(-0, 0.5) from ia32 and x64 platforms - we produce the correct value without bailing out.
Review URL: http://codereview.chromium.org/6532054

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6856 ce2b1a6d-e550-0410-aec6-3dcde31c8c00