Windows-compatibility: Complex syntax problem (Compound Solution Pack)

For some reason, when complex syntax {$...} is used, the code inside the curly braces sometimes doesn't get processed, resulting in error messages like: `"The file {$child->id}_TN.{$ext} cannot be found."` I'm not sure why this is happening, but concatenating the variables instead seems to fix the problem -- and should work with both Linux and Windows.

*NOTE:* The [Islandora Paged Content module](https://github.com/Islandora/islandora_paged_content/pull/42 "Windows-compatibility: Complex syntax problem (Islandora Paged Content)") is experiencing the same problem.