Changed the handling of Win32 function SetErrorMode to be more correct. The flag to prevent error dialogs is now merged with existing flags, and the error mode is now reset which it was not before.
Review URL: http://codereview.chromium.org/11471

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@792 ce2b1a6d-e550-0410-aec6-3dcde31c8c00