Fix MWMHints and -x option

On 64-bit systems, the -x/--borderless option was not functioning correctly. The issue is that the members of the MWMHints struct were declared as 32-bit types, while X11 expects longs for "format=32" fields.

From the XChangeProperty() man page: "If the specified format is 32, the property data must be a long array."

Additionally, mwmhints is now initialized to 0 to avoid sending uninitialized memory on to X11.