Fixed a few bugs from recent refactoring of FILES elements into objects of class DirEntry, and added caching for queries of
datasets within each experiment. By default, a cache time of 30 seconds is used, i.e. the query won't be re-run if it has been
run in the last 30 seconds. This cache timeout will be a command-line option soon...
Implemented caching for queries of datafiles within datasets.
Merge pull request #14 from wettenhj/master

Implemented caching for queries of datafiles within datasets