Converting dimensionless quantities back to plain numbers is errorprone #247

If n is an effectively dimensionless quantity, for instance

import quantities as pq
n = 3 * pq.s * pq.kHz

then one might reasonably want to convert n back to a simple number. To do so with error checking currently requires code along the lines of

n = (n - 0).simplified.magnitude

If I simply write

n = n.magnitude

the result is 3 rather than 3000, and

n = n.simplified.magnitude

does not catch errors if n is not dimensionless.

Simpler syntax would be useful.