Fix location filtering for example in nested group in shared group in external file

Created by: myronmarston

For examples defined in an example group in a shared example group in an external file, it did not work properly because the location filtering only considered the immediate parent example group’s file path, which did not match the passed location filter. By considering all parent example group file paths, it filters properly.

Fixes #835 (closed).

Note: this commit began from a failing spec that originated with @soulcutter and was fixed up by @xaviershay.