This warning is practically pointless, and since we treat warnings as errors on Appveyor, it imposes spurious back-and-forths to fix it when it occurs.
This warning is generated when a value that is not bool is assigned or coerced into type bool. Typically, this message is caused by assigning int variables to bool variables where the int variable contains only values true and false, and could be redeclared as type bool. If you cannot rewrite the expression to use type bool, then you can add "!=0" to the expression, which gives the expression type bool. Casting the expression to type bool does not disable the warning, which is by design.
This warning is no longer generated in Visual Studio 2017.