0027111: Add generalized copy constructor in handle class for old compilers

0027111: Add generalized copy constructor in handle class for old compilers

Copy constructor and assignment operator from handle of derived type is added in handle class.
They are enabled only if macro OCC_HANDLE_NOCASTS is defined, and operators of cast of handle to reference to handle to base type are disabled in that case.

Useless type casts to handle to base type are removed in GC and GCE2d classes.
Code returning reference to handle from function is corrected to return it either by value or as reference to handle of actual type.