Bug#1094385: matplotlib, pandas: build-depend cycle, unable to bootstrap

[Rebecca N. Palmer]

It's not going to be tonight, because my first few attempts didn't work. 
 If current Salsa builds, I intend to upload it in the morning.

(It did get far enough to find that there are two new test failures, one 
that should now be fixed and one that I'll file a separate bug about.)