The error cases were returning false instead of true.

The error cases were returning false instead of true.
So if the caller does something like:
while(!IdleNotification())
it could spin forever if v8 were not initialized.

I'd like to further remove the is_high_priority flag,
because it is not in use. Mads - is there any reason
not to remove it?

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3014 ce2b1a6d-e550-0410-aec6-3dcde31c8c00