[Cuis-dev] Integer>>lcm:

[Luciano Notarfrancesco]

Integer>>lcm: was defined in such a way that it could return negative
numbers. Also '0 lcm: 0' produced division by zero.

The least common multiple is unique "up to units", so to make it unique you
have to do a consistent choice of associate (negative or positive). For
integers it is customary to define LCM(a,b) to be 0 if a=0 or b=0, and
strictly positive otherwise. This is how it is defined in Magma, GAP and
GMP, etc, and this change set fixes Integer>>lcm: to behave like that.

I also attach some tests for Integer>>gcd: and Integer>>lcm:.
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