top: provide cmdline argument '-H' to enable thread scanning by default

top: provide cmdline argument '-H' to enable thread scanning by default

In particular useful when you want to evaluate the threads in batch mode:
    top -Hbn1

function                                             old     new   delta
top_main                                             928     941     +13
packed_usage                                       33317   33319      +2
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 15/0)               Total: 15 bytes

Signed-off-by: Philippe Belet <philippe.belet@nokia.com>
Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>