* Bug fix for range analysis (contributed by Andy Wingo). Ranges of
double values have to include negative zero. Original code review:
 http://codereview.chromium.org/7514040/

* Fix a bug in optimized Math.round on ARM. When emitting minus-zero checks
we previously return a wrong result because of incorrect register assignment.

* Fix performance problem in IA32 and x64. Refine the checks
for minus zero and avoid unnecessary deoptimizations on Math.floor.

* Improve mjsunit test for Math.round to make sure we also
 get the optimized version of the code for each test case.
Review URL: http://codereview.chromium.org/7604028

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8877 ce2b1a6d-e550-0410-aec6-3dcde31c8c00