Validate inputs are real for mesh, meshc, meshz functions. Rename internal helper variables for greater clarity. * scripts/plot/mesh.m: Validate inputs are real. Use htmp for temporary handle. * scripts/plot/meshc.m: Validate inputs are real. Use htmp for temporary handle. * scripts/plot/meshz.m: Validate inputs are real. Use htmp for temporary handle. Use cellfun to replace for loop in input validation. Use oldax for saved axes handle.