[Issue 9149] Disallow calling const delegates with a mutable context

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=9149

timon.gehr at gmx.ch changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Disallow converting         |Disallow calling const
                   |delegates to const          |delegates with a mutable
                   |                            |context

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