Fix compatibility with Boost 1.74
Fix compatibility with Boost 1.74

This patch adjust usage of Boost filesystem to account for the
deprecation of boost::filesystem::copy_option.

gridcoin/Gridcoin-Research,Git-Jiro/Gridcoin-Research,gridcoin/Gridcoin-Research,gridcoin/Gridcoin-Research,gridcoin/Gridcoin-Research,Git-Jiro/Gridcoin-Research,caraka/gridcoinresearch,caraka/gridcoinresearch,Git-Jiro/Gridcoin-Research,caraka/gridcoinresearch,caraka/gridcoinresearch,Git-Jiro/Gridcoin-Research,caraka/gridcoinresearch,caraka/gridcoinresearch,gridcoin/Gridcoin-Research,gridcoin/Gridcoin-Research,Git-Jiro/Gridcoin-Research