fix cross-compilation issue with Numpy
reorder the if's for clarity
fix GpuMat::copyTo method with mask:

fill destination matrix with zeros if it was reallocated
fix message sent to user during cross_compilation
Merge pull request #2175 from vrabaud:2.4
Merge pull request #2188 from jet47:gpumat-copyto-fix
removing duplicated legacy license, the actual instance is in 'opencv/LICENSE'
Merge pull request #2193 from apavlenko:2.4_lic_remove