found bug with empty destination directory;prevent checking for upload if plugin does not need to process files

added replacement of storage directory with data directory for the purpose of comparing original and storage file directory

modifications to eliminate processing of hidden files and of unchanged files that were processed already; checksum is now done by default

fixed few issues found while testing gridftp plugin and file observer; made observer more generic by shifting some functionality to agent

changed file processing interface; added support for relative file paths (with respect to daq directory)