PrecomputedKernelMatrixKernel now implements Copyable (so that shallow copies can be made) and Kernel.makeCopy and Kernel.makeCopies now check for Copyable before using deep copying via serialization

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka/trunk@9893 e0a1b77d-ad91-4216-81b1-defd5f83fa92
Merge remote-tracking branch 'upstream'