Fold mkpasswd applet into cryptpw.

Fold mkpasswd applet into cryptpw.
mkpasswd is in Debian, OTOH cryptpw was added to busybox earlier.
Trying to make both camps happy by making those two applets just aliases.
They are command-line compatible. We can decide whether we want to drop one
(and which one) later.

function                                             old     new   delta
cryptpw_main                                         183     314    +131
static.methods                                        21       -     -21
packed_usage                                       25707   25648     -59
mkpasswd_main                                        307       -    -307
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 1/1 up/down: 131/-387)         Total: -256 bytes