Fixing bugs after change of tnlVector interface.

src/matrix/tnlMultiDiagonalMatrix.h

src/mesh/tnlGrid.h

src/solvers/tnlBICGSolver.h

src/solvers/tnlBICGStabSolver.h

src/solvers/tnlCGSolver.h

src/solvers/tnlEulerSolver.h

src/solvers/tnlGMRESSolverOld.h

src/solvers/tnlILUPreconditioner.h

src/solvers/tnlMersonSolver.h

src/solvers/tnlPETSCPreconditioner.h

src/solvers/tnlPETSCSolver.h

src/solvers/tnlSORSolver.h

tests/unit-tests/solver/tnlMersonSolverTester.h