[Report] FileSystemPaths filter creates wrong directory for "Pragma: \define" tiddler

[pmario]

Tiddler Pragma: \define (tagged Pragmas) is matched by filter [tag[Pragmas]addprefix[pragmas/]] in $:/config/FileSystemPaths.

Actual behaviour on Windows: creates dir tiddlers/pragmas/Pragma_ / with file define.tid.
Expected: tiddlers/pragmas/Pragma_ _define.tid.

This is caused by $tw.utils.generateTiddlerFilepath (core-server/filesystem.js:356) does not sanitise \ in its cross-platform-filename regex.

PR with new tests on the way.