Protobuf: added requests for Cholesky decomposition and forward/backward substitution
PNaClContext: added cholesky and solveTriangular methods
WebWorkerContext: added cholesky and solveTriangular methods
PBContext: added cholesky and solveTriangular methods
JSContext: remove debug check for null data buffer in solveTriangular
JSWorker: implement cholesky and solveTriangular backends
PNaCl: stubs for CholeskyDecomposition and SolveTriangular requests