region files with ".reg.txt" extension should be parsed using region.file not region.textfile

[mawilson1234]

When the extension of the regions file is ".reg.txt", it gets parsed using region.textfile, which is incorrect. It should get parsed using region.file. Renaming the file to *.reg works, but this isn't great on Windows since that's used for registry files. The relevant code is experiment.py lines 54-57.