an obscure, undocumentated feature so no test was added. Closes
issue #1101399.

There should be no other effect than a small decrease in memory use.
Patch by Christopher Tur Lesniewski-Laas.

code, adds checks for stdin/out/err, cwd, and sys.path, and adds a new
section in the summary for tests that modify the environment (thanks to
Ezio Melotti for that suggestion).

makeunicodedata now generates double literals