Add Vector == ZZ method

Allows calling "zero" to determine test whether a vector is the zero
vector.

Also add a unit test.

Author: d-torrance

M2/Macaulay2/m2/matrix.m2

@@ -119,6 +119,7 @@ Matrix == Matrix := (f,g) -> (
 Matrix == Number :=
 Matrix == RingElement := (m,f) -> m - f == 0		    -- slow!
 Matrix == ZZ := (m,i) -> if i === 0 then rawIsZero m.RawMatrix else m - i == 0
+Vector == ZZ := (v,i) -> matrix v == i
 
 Matrix + Matrix := Matrix => (
      (f,g) -> map(target f, source f, reduce(target f, raw f + raw g))

M2/Macaulay2/tests/normal/vector.m2

@@ -14,6 +14,8 @@ v = vector(N, {1, 2, 3})
 w = vector(N, {4, 5, 6})
 assert Equation(v, vector map(N,, {{1}, {2}, {3}}))
 
+assert zero vector {0, 0, 0}
+
 -- module operations
 assert Equation(+v, v)
 assert Equation(v + w, vector(N, {5, 7, 9}))