* ecore.cs (MemberLookupFinal): new version with all the
parameters customizable.
* expression.cs (New.DoResolve): Use MemberLookupFinal to locate
constructors. Return if the result value is null (as the error
would have been flagged already by MemberLookupFinal)
Do not allow instances of abstract classes or interfaces to be
created.
(Method.Emit): If the method is marked abstract and has a body,
emit an error.
svn path=/trunk/mcs/; revision=4577
