OCL StereoBM and images needing negative minimum disparity

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If minDisp is not available, you can shift one of your images left or right by the amount you would have used for minDisp. After doing the BM, you can then subtract/add the same amount to the results to compensate.

StereoBM has a state member that points to a CvStereoBMState. The CvStereoBMState has a member called minDisparity. If you have a StereoBM variable called bm, you just need to set bm.state->minDisparity to the value you want.

EDIT: I might be wrong about the OCL version. This is what works in the regular (cpu) version of StereoBM.