wget: implement -T SEC; rework progress meter to not use signals (it was unsafe)

wget: implement -T SEC; rework progress meter to not use signals (it was unsafe)

function                                             old     new   delta
retrieve_file_data                                   364     450     +86
bb_progress_update                                   615     682     +67
packed_usage                                       27406   27422     +16
wget_main                                           2440    2453     +13
static.wget_longopts                                 145     155     +10
progress_meter                                       199     159     -40
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 5/1 up/down: 192/-40)           Total: 152 bytes

Signed-off-by: Bradley M. Kuhn <bkuhn@ebb.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>