Scoping issue in cnn_qp1_mpii.m

[Neilerino]

Hey! I was interested in your project, so I tried training the model myself, and I found a very small scoping bug that might've come up from a new matlab version.

In cnn_qp1_mpii.m in the function getImageStats you try and access avg, rgbm1, rgbm2 out of the scope of the for loop. Very simple fix, you just have to declare the variables in that function before the for loop, so that they are in the functions main scope.
I can open the pull request if this actually an issue :)
Great job!