diff: rewrite. much smaller and more correct

diff: rewrite. much smaller and more correct

function                                             old     new   delta
diffreg                                             1815    3156   +1341
diff_main                                            860    1194    +334
read_token                                             -     161    +161
skip_dir                                               -      44     +44
seek_ft                                                -      31     +31
fetch                                                362     392     +30
line_compar                                            -      21     +21
add_to_dirlist                                        65      61      -4
print_only                                            16       -     -16
skipline                                              51       -     -51
newcand                                               85       -     -85
asciifile                                             89       -     -89
print_status                                         178      73    -105
make_temp                                            148       -    -148
files_differ                                         168       -    -168
get_recursive_dirlist                                182       -    -182
sort                                                 226       -    -226
prepare                                              283       -    -283
change                                               283       -    -283
do_diff                                              416       -    -416
dump_unified_vec                                     457       -    -457
check                                               1512     595    -917
------------------------------------------------------------------------------
(add/remove: 4/12 grow/shrink: 3/3 up/down: 1962/-3430)     Total: -1468 bytes

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>