ls: reorder and rename functions. No code changes

ls: reorder and rename functions. No code changes

function                                             old     new   delta
display_single                                         -     931    +931
scan_and_display_dirs_recur                            -     497    +497
display_files                                          -     422    +422
showfiles                                            422       -    -422
showdirs                                             497       -    -497
list_single                                          931       -    -931
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(add/remove: 3/3 grow/shrink: 0/0 up/down: 1850/-1850)          Total: 0 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>