rust: fix file folding map...
rust: fix file folding map
The file folding map, frequently used on macOS, had two issues:
* the means for converting it to Python didn't work
* a minor typo when copying the python code, where `!=` became `==`
With this, the rust code passes all tests on macOS.
Test Plan:
I'm currently doing a full test run on a case-insensitive file system. If it passes, perhaps we can change the platform check from an error to a warning?
Differential Revision:
https://phab.mercurial-scm.org/D9671
