[ODE] Autotools support

[J. Perkins]

On 3/15/06, J. Perkins <starkos at gmail.com> wrote:
> The config.h generated by the autotools script must also define
> this symbol (ODE_API) or the build will break.

FYI, I found where this is defined and made the change. I add `ODE_`
before the DLL_EXPORT symbol to help prevent conflicts with any
user-defined symbols.

I've got a bit more cleanup and testing to do, then I will check
everything in. Probably tonight or tomorrow.

Jason