portability fix for pow overload resolution
portability fix for pow overload resolution

On Solaris the compiler is missing the template overload.

toolking/AMQP-CPP,CopernicaMarketingSoftware/AMQP-CPP,CopernicaMarketingSoftware/AMQP-CPP,fantastory/AMQP-CPP,toolking/AMQP-CPP,fantastory/AMQP-CPP