Handle duplicate file basenames when testing multiple files in parallel

[mpatel]

When we test

/path/to/foo.py

sage-doctest writes

SAGE_TESTDIR/.doctest_foo.py

runs the new file through python, and deletes it. This can cause collisions when we test in parallel multiple files with the same basename, e.g., __init__, all, misc, conf, constructor, morphism, index, tests, homset, element, twist, tutorial, sagetex, crystals, cartesian_product, template, ring, etc.

There's a similar problem with testing non-library files, which sage-doctest first effectively copies to SAGE_TESTDIR.

See ​sage-devel for background.

This ticket may help with some of the doctesting problems discussed on the Sage mailing lists. Related tickets: #9224, #9225, #9449.

[mpatel]

William Stein ​suggests:

Could we use the tempfile module instead of using SAGE_TESTDIR.  The
tempfile module makes files and directories by default that are unique
and are *designed* to live on a fast filesystem, which gets cleaned
regularly.

sage: import tempfile 

[mpatel]

Frequency-sorted list of doctest file basenames (includes .py, .pyx, .pxi, .rst, .tex files). Not a patch.