Better Windows support

[spaze]

This release adds better Microsoft Windows support. Some extension functionality ("allow calls in") didn't work properly until now.

• It all started with Disable backslash escaping in "is allowed" helper (Disable backslash escaping in "is allowed" helper #169, thanks @mnastalski)
• Then I Make tests pass on Windows™ too Make tests pass on Windows™ too #170
• And then I made an internal-only change Correct allow path in tests Correct allow path in tests #171

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This discussion was created from the release Better Windows support.