Allow resolution of relative paths in tool data configuration and loc files.
The string ${__HERE__} will be expanded out to the directory the file (XML configuration or loc) currently resides in.

Along with some changes to planemo to detect test data files (https://github.com/galaxyproject/planemo/commit/a40130417dc1be2da785cd5dff64909986d045a0) - the following picard tweak demonstrates how tool developers could use this to build test cases for cached/index data (https://github.com/jmchilton/picard/commit/4df8974384081ee1bb0f97e1bb8d7f935ba09d73).
Merge next-stable.
Fix boolean handling for workflow editor
Merge