1. added option to import empty sub-directories (previously empty subdirs were
    always ignored).
2. attempt to generate a unique internal code when the auto-generated internal
    code (based on the characters in path) is not unique.
3. display "Scannnig Directories..." popup since this can take a while
    (especially on network drives and especially recurisvely).

Note: if you're importing lots of deeply nested subdirs, it's likely that a
unique internal code can't be generated (from the path) for all subdirs.
A randomly generated internal code might be an option if this is really
a problem for any sysops.

Also updated the brace style of this .c file, finally.