File Selection

This is a general purpose file selection tool that is used in several
different places within Pablo.  It is used to select files and
directories for loading and saving configurations and layouts, as well
as specifying files related to the File Input and File Output modules. 
Regardless of the specific use, this file selection dialog behaves in the
same way.

The filter text window is used to specify a directory path and file
specification to determine which directories and files to show to the
user. The directory list shows all directories that are below the
present directory (as well as the present directory and its parent),
and the file list shows all files that meet the filter specification.
Note that UNIX directories are simply files, so all directories will 
also be in the file list.  

The directory hierarchy is traversed by selecting a directory in the
directory list and choosing FILTER.  This effectively moves into that
directory and finds all files in that directory that meet the filter
requirements.  Double clicking on a directory does the same thing as
choosing FILTER.  Choosing a file from the file list causes that file
to be selected, and that file is show in the selection text field.  Once
the desired file is chosen, selecting OK will cause the selected file to
be used for whatever purpose the file selection dialog was used.  Double
clicking on the file will do the same thing as choosing OK.  
