Fix Math.pow(-0, 0.5) and Math.pow(-0, -0.5).  These are not equal to sqrt(-0) and 1/sqrt(-0).  Add tests for these cases.  Fixes V8 issue 1088.
BUG=1088
TEST=test/mjsunit/math-pow.js

Review URL: http://codereview.chromium.org/6368050

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6573 ce2b1a6d-e550-0410-aec6-3dcde31c8c00