Incorrectly implemented list-ing of Index

Change __list__ method to __iter__ yielding filenames to allow built-in list of Index object

Signed-off-by: Joseph Lee <josephl@cecs.pdx.edu>
Fixed list generation of tree

Signed-off-by: Joseph Lee <josephl@cecs.pdx.edu>
Removed pdb.set_trace()

Signed-off-by: Joseph Lee <joseph@idealist.org>
Changed list generator to recursive generator method

Signed-off-by: Joseph Lee <joseph@idealist.org>