ash,hush: improve randomness of $RANDOM, add easy-ish way to test it

function                                             old     new   delta
next_random                                           68     113     +45
change_random                                        103     121     +18

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
random: cosmetic tweaks in debug code

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
hush: make "true" built-in

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ash,hush: fix a thinko about 2^64-1 factorization

function                                             old     new   delta
next_random                                          113     119      +6

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
sherpya: android port
added my default config