Fix small bug in ns-registry auto creation

[jhiemstrawisc]

We talked this morning about config variables that specify "Location" and how they should specify the actual filename. I had previously tried to implement some logic that if a file location was passed such as /foo/bar/, the namespace registry would auto create the registry database as /foo/bar/ns-registry.sqlite. Instead of fixing the bug in that logic, let's just say whatever is passed should be considered the file name. A side effect of this is that if the user configures NSRegistryLocation = /foo/bar/, the file will be created as /foo/bar/.sqlite because the code automatically adds a file extension when none is provided and in this case, the actual filename is empty.

This fixes #67

[bbockelm]

I don't particularly love the "magic addition of the .sqlite extension" here. If the user wants to call it foo, it should be foo -- don't surprise them with foo.sqlite.

That said, my gripe isn't part of this PR... so approving. Just wanted to share the "philosophy" here for the future.