Bug#864364: freemat: toolbox missing diff() and run_tests()

[Graham Inggs]

Control: tags -1 + pending

These files are not very big, so instead of generating a new tarball,
we can restore them with a patch until the next upstream release.  I
have pushed this to git [1], as well updating Files-Excluded, and
enabling the diff() and hist() tests.
Please let me know if you have any objections to this approach.

[1] https://anonscm.debian.org/cgit/debian-science/packages/freemat.git/commit/?id=0b8cf010e3f58afe222a36b644c896d77ed945e6