Tighten up integer division checks on Quantity

[chiphogg]

This test fails:

EXPECT_EQ(hertz(100), 1 / milliseconds(10));

It should fail to compile. (i.e., the goal is to expand our integer division check to include the cases where only one argument is a Quantity.)

[chiphogg]

By the way, and for posterity: here's how we could get that test to pass:

EXPECT_EQ(hertz(100), inverse_as(hertz, milli(seconds)(10)));

This would automatically divide the value 10 into 1000, because hertz times milli(seconds) gives a dimensionless unit whose magnitude is 1/1000.