Bug#826095: python-pandas: please provide backport of pandas

[Rebecca N. Palmer]

A potential problem is that upgrading pandas breaks some of its reverse 
dependencies: whether this is a blocker for backports is being discussed 
at https://lists.debian.org/debian-backports/2020/04/threads.html#00062

Packages thought to break are
cnvkit influxdb-python snakemake statsmodels tqdm
with pandas 0.25, plus
dask python-biom-format seaborn
if later upgraded to 1.0.  However, this is based on transition testing 
in unstable (#931557 / #950430), so there may be more in buster.

It would probably also be necessary to backport some of pandas' (build) 
dependencies, and at least pytest would involve similar breakage.

The Neurodebian backports mentioned above stop at 0.23, which current 
stable already has.