The file resource has been updated.  There are now three types of files: (1) files whose content is stored on the filesystem of the server, (2) files that refer to other (A/V) files for their content (have a parentFile attribute), (3) files whose content is stored elsewhere (have a url attribute).  Also, files can now be updated using the multipart/form-data content-type.
Added two new test files to the test_files directory.
Improved the SQLAQueryBuilder module/class so that relational properties of objects (both scalars and collections) can be searched more thoroughly; e.g., one can now search for subinterval-referencing files by their parentFile scalar relation: ["File", "parentFile", "MIMEtype", "=", "audio/x-wav"].