conv does not preverve orientation of input

[Moritz Borgmann]

In Octave, the orientation of the output of y = conv(a,b) is always a 
row vector. In Matlab, the rules are the following:

 - if a is shorter or equal in size to b: orientation of y is the same as b
 - if b is shorter than a: orientation of y is same as a.

Wuut. You may or may not believe it, but there's code that depends on 
this behavior. Find attached a patch that "fixes" conv.m.

Test cases are included.

-M

mb-fix-conv.changeset
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