StringToInt rewritten. This version doesn't allocate memory for long decimals and uses percise rounding if radix 10 or a power of 2 (in other cases rounding error still may occur). Handling special values moved from Runtime_StringParseInt into StringToInt in order to make it consistent with StringToDouble.

Review URL: http://codereview.chromium.org/1529004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4329 ce2b1a6d-e550-0410-aec6-3dcde31c8c00