tree: new applet

Adds the tree program to list directories and files in a tree structure.

function                                             old     new   delta
tree_print                                             -     343    +343
scandir64                                              -     330    +330
scandir                                                -     330    +330
tree_main                                              -      86     +86
.rodata                                           105150  105228     +78
packed_usage                                       34511   34557     +46
alphasort64                                            -      31     +31
alphasort                                              -      31     +31
strcoll                                                -       5      +5
applet_names                                        2801    2806      +5
applet_main                                         1616    1620      +4
applet_suid                                          101     102      +1
applet_install_loc                                   202     203      +1
------------------------------------------------------------------------------
(add/remove: 11/0 grow/shrink: 6/0 up/down: 1291/0)          Total: 1291 bytes

Signed-off-by: Roger Knecht <rknecht@pm.me>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>