Bug#931557: transition: pandas 0.23 -> 0.25

[Rebecca N. Palmer]

Control: block -1 by 937236
(0.25 is Python 3 only)

I have now done a build test with the new python3-pandas installed:

Success:
bcbio caffe cnvkit dask dask.distributed drms igdiscover lmfit-py 
matplotlib mirtop nbsphinx partd patsy poliastro pynwb python-airr 
python-apptools python-biom-format python-cobra python-fluids 
python-geopandas python-geotiepoints python-pybedtools python-pymeasure 
python-tablib python-treetime python-ulmo python-xarray q2-cutadapt 
qiime scikit-learn seaborn sklearn-pandas snakemake spyder-kernels

*FTBFS with new pandas*: python-feather-format python-skbio statsmodels

FTBFS with or without new pandas: keras pysal rdkit sunpy

snakemake's autopkgtest issue appears to have been fixed, but cnvkit and 
q2-types are still listed as failing.  (The above build test was just a 
build, not autopkgtests.)