mtlb_prod Matlab prod emulation function

## Description

Matlab and Scilab `prod` behave differently in some particular cases:

- When called with one input: Matlab `prod` treats the values along the first non-singleton dimension of input while Scilab `prod` threats all values of input.

- When called with two inputs: Matlab `prod` can be used with second input giving a non-existing dimension of first input while Scilab `prod` returns an error message.

The function `mtlb_prod(A[,dim])` is used by `mfile2sci` to replace `prod(A[,dim])` when it was not possible to know what were the inputs while porting Matlab code to Scilab. This function will determine the correct semantic at run time. If you want to have a more efficient code it is possible to replace `mtlb_prod` calls:

- When called with one input, if `A` is an empty matrix, a scalar or a vector, `mtlb_prod(A)` may be replaced by `prod(A)`

- When called with one input, if `A` is a not-empty matrix, `mtlb_prod(A)` may be replaced by `prod(A,1)`

- When called with one input, if `A` is a multidimensional array, `mtlb_prod(A)` may be replaced by `prod(A,firstnonsingleton(A))`

- When called with two inputs, if `dim` is lesser than the number of dimensions of `A` `mtlb_prod(A,dim)` may be replaced by `prod(A,dim)`

Caution: `mtlb_prod` has not to be used for hand coded functions.

## See also

- firstnonsingleton