moved intd to base directory

The intd (indefinite integral) function is moved out of
the @mvpoly_cube directory into the base directory since
it does not depend on the cube representation, just on the
mvpoly polynomial object methods.

The kronn (multi-argument kron) function, needed by Matlab
is used by intd so it is moved from @mvpoly_cube/private to
the base directory.
random seed fixed for multiply tests

The test "multiply distribute over evaluate" was subject
to occasional failure due to inaccuracy for some random
inputs. Added a call to rand('seed', 42) to fix the
matrix passed to this test.