awk: improve nadling of negative numbers in bitwise ops;

awk: improve nadling of negative numbers in bitwise ops;
 fix handling of octal costants. add test for it

function                                             old     new   delta
getvar_i_int                                           -      93     +93
my_strtod                                              -      84     +84
qrealloc                                              33      36      +3
getvar_i                                              99      95      -4
next_token                                           979     919     -60
evaluate                                            6359    5627    -732
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 1/3 up/down: 180/-796)         Total: -616 bytes