[Issue 18985] bad error message for += operation on shared Object

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18985

--- Comment #2 from OlegZ <black80 at bk.ru> ---
yes, the error disappeared.
for non-shared vars should be used non-shared method overloading (when it
needed) or non-shared another class. not easy.
and about to change wrong error text I filled before another bug/enhancement
https://issues.dlang.org/show_bug.cgi?id=18961 (second comment)

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