Bug#943732: pandas: high RAM usage in test suite

[Rebecca N. Palmer]

Control: retitle -1 pandas: high RAM usage in test suite
Control: severity -1 normal

The ones I've tried (~half the affected ones) pass on qemu-mipsel when 
run in smaller batches.

Memory usage for the whole test suite (on amd64) starts at nearly 1GB 
just for *collecting* the tests and continues to rise during the test 
suite run.  (I don't know if this is a memory _leak_ or the normal 
result of such a large (~61k items) test suite.)

Given the above, I suspect the MemoryErrors are this cumulative memory 
use, not any single test using too much, and hence that the issue can be 
fixed by splitting up the test suite.

(The new failures on arm*/ppc64 are a time zone conversion test using 
now() as input, which these architectures happened to build during a DST 
transition => AmbiguousTimeError.)