Fix a regression for deletion of Alias() objects.

Fixes a regression introduced by commit 694dea6. In the case of
Alias namespace nodes, the node simply points to the aliased node via
the Object field; thus we cannot assume that the object is an
operand object.

Affects core ACPICA and the ACPICA tools including iASL and
acpiexec.
Merge branch 'master' of ssh://ssh.github.com/acpica/acpica