install OpenCV headers when using local OpenCV

[birarda]

This adds the OpenCV headers to installed headers when using a local OpenCV. Using the PSMoveTracker requires the presence of these headers to write a frame to the OpenCV window.

[thp]

Yes, I guess this makes sense, since the only way to retrieve the tracker image at the moment is as an IplImage *. If we ever get around to support different backends for the tracking algorithm, we might have to change this, but until then, this looks good (also it's only done when linking against a local OpenCV build, so building against a system-installed OpenCV won't change behavior here).

[cboulay]

Sorry I didn't really know what was going on here when this PR was made so I couldn't comment, but I understand it better now and I have a question.

While it's true that currently the only way to use the result of psmove_tracker_get_frame is with OpenCV, by providing the headers in psmoveapi's include folder you are implying that psmoveapi also exposes the symbols associated with those headers. Does it? I don't really understand this process.

If it does not, then I don't think the headers should be copied to the include folder. Anyone hoping to do anything useful with the void* returned by psmove_tracker_get_frame can be expected to already have included and linked their own OpenCV anyway.

[birarda]

We're not using psmoveapi anymore, so my memory may be foggy on this - for our use case I wasn't actually needing to do anything useful with the result of psmove_tracker_get_frame but I could not compile code hoping to present the capture window for debugging (which didn't seem to suggest that OpenCV headers be findable on the system by compiler) without installing the OpenCV headers and getting those into my build.