Initial commit for new dw_signal_connect_data() function... Same as dw_signal_connect() but it has an additional callback parameter that gets called when the callback is being removed. This allows me to free memory allocated for the data parameter and prevent memory leaks in godwindows... Tested GTK and Mac.

# Set these here to change the version for all platforms
DW_MAJOR_VERSION=2
DW_MINOR_VERSION=5