Don't generate default cypclass __alloc__ when user provides it

Cython/Compiler/ModuleNode.py

@@ -1120,7 +1120,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 code.putln("%s(){}" % type.cname)
                 code.putln("// Generating __alloc__ function (used for __new__ calls)")
                 alloc_entry = scope.lookup_here("<alloc>")
-                code.putln("static %s { return new %s(); }" % (alloc_entry.type.declaration_code(alloc_entry.cname), type.declaration_code("", deref=1)))
+                if alloc_entry.is_builtin_cmethod:
+                    code.putln("static %s { return new %s(); }" % (alloc_entry.type.declaration_code(alloc_entry.cname), type.declaration_code("", deref=1)))
             code.putln("};")
 
         if type.is_cyp_class:

Cython/Compiler/Symtab.py

@@ -699,7 +699,11 @@ class Scope(object):
                 alloc_name = "<alloc>"
                 alloc_entry = scope.declare(alloc_name, alloc_cname, alloc_type, pos, visibility)
                 alloc_type.entry = alloc_entry
+                alloc_entry.is_inherited = 1
                 alloc_entry.is_cfunction = 1
+                # is_builtin_cmethod is currently only used in cclass, so it should be safe
+                # to use it here to distinguish between implicit default __alloc__ and user-defined one
+                alloc_entry.is_builtin_cmethod = 1
                 alloc_entry.func_cname = "%s::%s" % (entry.type.empty_declaration_code(), alloc_cname)
 
         if self.is_cpp_class_scope: