[patch] for Implicit/Explicit generic class operators

Original Reporter info from Mantis: hnb

• Reporter name: Maciej Izak

Description:

Another patch from hated SmartPointers effort ;). Very important part for TSmartObj.Implicit:

https://github.com/maciej-izak/PascalSmartPointers/blob/master/SmartObj.pas

Without patch FPC raise error: "Impossible to overload assignment for equal types."
Patch is also Delphi compatible.

Test and patch attached.

Mantis conversion info:

• Mantis ID: 30534
• Version: 3.1.1
• Fixed in version: 3.1.1
• Fixed in revision: 34526 (#0500c678), 35740 (#ff28d5c8)