Bug#950430: numpy 1.19 vs pandas 1.0

[Rebecca N. Palmer]

Numpy 1.19 is currently an ~rc in experimental, and recently became 
final upstream.

Both pandas 0.25.x and 1.0.x currently FTBFS with numpy 1.19, but I 
think 1.0.x is fixed in Salsa, while 0.25.x looks doable but more work. 
(It has a build failure that looks like 
https://github.com/pandas-dev/pandas/issues/30709, and 37 test failures 
that are mostly complaints about new warnings or reworded error messages.)

Hence, it would be nice but probably not essential to get pandas 1.0.x 
to unstable before numpy 1.19.