Fix xmalloc_fgets_str so that it really does NOT strip terminator.

Fix xmalloc_fgets_str so that it really does NOT strip terminator.
Add xmalloc_fgetline_str which does strip terminator,
and use it in dpkg instead of xmalloc_fgets_str.
netstat: use xmalloc_fgets_str - allows to eat strings with NULs
(this fixes bug with some weird /proc/net/unix input)

function                                             old     new   delta
xmalloc_fgets_internal                                 -     191    +191
xmalloc_fgetline_str                                   -      18     +18
do_info                                              116     120      +4
unix_do_one                                          451     447      -4
tcp_do_one                                           423     419      -4
send_tree                                            369     365      -4
xmalloc_fgets_str                                    178      15    -163
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 1/4 up/down: 213/-175)           Total: 38 bytes
   text    data     bss     dec     hex filename
 778445     832    7344  786621   c00bd busybox_old
 778483     832    7344  786659   c00e3 busybox_unstripped