Win32 warning compilation

include/Keithley_6485.h

include/Keithley_6487.h

include/Keithley_6514.h

include/Keithley_6517.h

src/Keithley_6485.cpp

src/Keithley_6487.cpp

src/Keithley_6514.cpp

src/Keithley_6517.cpp