#17 Category and collide bits using variable-sized data type

[Jason Perkins]

The Geom category and collide bits are defined as
unsigned long. To my understanding, this data type
could vary in size on 32- and 64-bit platforms. This
should be changed to use one of the well-defined data
types from config.h, probably uint32.

This is an issue for language bindings (Java, .NET,
etc.) and for pre-built DLLs that might get used on a
64-bit system.