Fix two reference leaks that could occur following an obscure error

[jamadden]

Fixes #143

Based on #145 (to avoid the guaranteed conflict in CHANGES.rst), only the last commit is relevant.

[mgedmin]

The travis failure is probably unrelated:

+ auditwheel repair wheelhouse/persistent-4.6.4.dev0-cp27-cp27m-linux_x86_64.whl -w /io/wheelhouse/
Traceback (most recent call last):
  File "/usr/local/bin/auditwheel", line 8, in <module>
    sys.exit(main())
  File "/opt/_internal/cpython-3.7.7/lib/python3.7/site-packages/auditwheel/main.py", line 50, in main
    rval = args.func(args, p)
  File "/opt/_internal/cpython-3.7.7/lib/python3.7/site-packages/auditwheel/main_repair.py", line 49, in execute
    from .repair import repair_wheel
  File "/opt/_internal/cpython-3.7.7/lib/python3.7/site-packages/auditwheel/repair.py", line 14, in <module>
    from .wheeltools import InWheelCtx, add_platforms
  File "/opt/_internal/cpython-3.7.7/lib/python3.7/site-packages/auditwheel/wheeltools.py", line 17, in <module>
    from wheel.wheelfile import WHEEL_INFO_RE  # type: ignore
ModuleNotFoundError: No module named 'wheel.wheelfile'
The command "bash .manylinux.sh" exited with 1.

[jamadden]

The travis failure is probably unrelated:

• auditwheel repair wheelhouse/persistent-4.6.4.dev0-cp27-cp27m-linux_x86_64.whl -w /io/wheelhouse/ File "/opt/_internal/cpython-3.7.7/lib/python3.7/site-packages/auditwheel/wheeltools.py", line 17, in from wheel.wheelfile import WHEEL_INFO_RE # type: ignore ModuleNotFoundError: No module named 'wheel.wheelfile' The command "bash .manylinux.sh" exited with 1.

Yes, that's a known issue since manylinux updated to auditwheel 3.1 6 days ago. https://github.com/pypa/manylinux/issues/512

[jamadden]

Upstream issue has been fixed, build caches have been cleared, new images downloaded, and the build is now green.

Thanks!