Fix parsing for .properties files with - in path

[jdpopkin]

This adds a test that repros the problem in #974 and fixes it, at least for this specific filetype. The fix just involves changing the maximum file extension length for one of the regexes. The same problem would still happen to files with longer extensions.

There's probably a small tradeoff between performance and file extension length, and there will probably always be someone out there who wants to use even longer file extensions. But I think .properties is worth supporting - it's a common enough filetype to have its own Wikipedia article.

[dandavison]

Thanks @jdpopkin! I agree this should be fixed and your solution LGTM. I'll merge when the tests pass.