Search for default views isn't restrictive and gets confused by *.view.php~ and friends

I introduced this bug over at #460248: Split default views into separate files. Inside project_issue_views_default_views() when we're doing the file_scan_directory(), we need to be careful so we don't read both foo.view.php and foo.view.php~ etc. That results in duplicate views, which confuses views and makes it think your view is always overridden and can't be reverted. See #921210: Fix performance of "My issues" as an example of where I was nailed by this in practice. ;)
Trivial fix, just opening an issue to document the commit.