Add conditional support for -v / --verbose

With FEATURE_VERBOSE off, practically no size change.
With it on:

function                                             old     new   delta
remove_file                                          493     556     +63
install_main                                         719     765     +46
bb_make_directory                                    383     419     +36
rmdir_main                                           162     191     +29
copy_file                                           1516    1544     +28
mv_main                                              502     525     +23
cmp_main                                             677     693     +16
bbconfig_config_bz2                                 5264    5279     +15
mkdir_main                                           158     168     +10
install_longopts                                      66      76     +10
rm_main                                              167     175      +8
nexpr                                                840     846      +6
scan_tree                                            275     280      +5
fsck_main                                           1807    1811      +4
ed_main                                             2541    2545      +4
expand_one_var                                      1574    1575      +1
swap_on_off_main                                     420     418      -2
parse_command                                       1443    1440      -3
redirect                                            1279    1274      -5
do_load                                              946     918     -28
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 16/4 up/down: 304/-38)          Total: 266 bytes

Based on the patch by Igor Živković.

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