Add PlainObjectBase copy ctor from PlainObjectBase and DenseBase objects. (manual backport from default branch, fix segfault when creating PlainObjectBase object, though such an usage is not recommended at all)
Add PlainObjectBase copy ctor from PlainObjectBase and DenseBase objects. (manual backport from default branch, fix segfault when creating PlainObjectBase object, though such an usage is not recommended at all)

--HG--
branch : 3.2

robustrobotics/eigen,robustrobotics/eigen,robustrobotics/eigen,robustrobotics/eigen