Efficiency change. Store a single matrix of data instead of vectors.

Normally it should still be possible to instantiate dseries objects
from mat files generated by previous versions of Dynare (before 4.6).
3 jobs for master in 1 minute and 32 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #10782
test_matlab

00:00:46

passed #10784
test_octave

00:01:31

passed #10783
test_old_matlab

00:01:00