Bug #50820.

Bug #50820.
* typemanager.cs (closure_private_ok, closure_invocation_type)
(closure_qualifier_type, closure_invocation_assembly)
(FilterWithClosure): Move to ...
(Closure): New internal nested class.
(Closure.CheckValidFamilyAccess): Split out from Closure.Filter.
(MemberLookup, RealMemberLookup): Add new almost_match parameter.
* ecore.cs (almostMatchedMembers): New variable to help report CS1540.
(MemberLookup, MemberLookupFailed): Use it.
* expression.cs (New.DoResolve): Treat the lookup for the
constructor as being qualified by the 'new'ed type.
(Indexers.GetIndexersForTypeOrInterface): Update.

svn path=/trunk/mcs/; revision=28761