hwclock: size optimizations
libbb/time.c: new file, introducing monotonic_us()
pscan, traceroute, arping: use it instead of gettimeofday
ping, zcip: TODO

function                                             old     new   delta
monotonic_us                                           -      89     +89
find_pair                                            164     180     +16
.rodata                                           129747  129763     +16
refresh                                             1144    1152      +8
............
timeout                                                8       4      -4
static.start                                           8       4      -4
last                                                   8       4      -4
parse_conf                                          1303    1284     -19
time_main                                           1149    1124     -25
gettimeofday_us                                       39       -     -39
arping_main                                         2042    1969     -73
hwclock_main                                         594     501     -93
catcher                                              485     380    -105
traceroute_main                                     4300    4117    -183
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 8/11 up/down: 157/-562)        Total: -405 bytes

diff --git a/libbb/Config.in b/libbb/Config.in
index a1ff7c0..0a3769d 100644
--- a/libbb/Config.in
+++ b/libbb/Config.in
@@ -95,4 +95,14 @@
 	  Setting this option allows for prompts to use things like \w and
 	  \$ and escape codes.
 
+config MONOTONIC_SYSCALL
+	bool "Use clock_gettime(CLOCK_MONOTONIC) syscall"
+	default y
+	help
+	  Use clock_gettime(CLOCK_MONOTONIC) syscall for measuring
+	  time intervals (time, ping, traceroute etc need this).
+	  Probably requires Linux 2.6+. If not selected, gettimeofday
+	  will be used instead (which gives wrong results if date/time
+	  is reset).
+
 endmenu