6lowpan: add notes to CHANGES and radvd.8.man

Conflicts:
	CHANGES
sllao: clean up readability of sllao in send.c

This code was not commented and it was unclear.  This made it
challenging for 6lowpan code to be added (as the hardware address
is not the same size as standard ethernet).  Hopefully this change
will make the intent of the sllao code clear.
rename radvdion.c readn_writen.c
syscalls_test.c: flesh out radvd_bind

just return 0 for success
add config.h.in~ to .gitignore
always write a pid file if specified on command line

When running tests, we need a reliable way to find the radvd pid so we can
reliably kill radvd.  Write a pidfile, or die, if the -p option is passed
to radvd.
add trivial radvd run check
timer.c: prune expired

coverage testing exposed the function, expired, as never called.
use ppoll to prevent signal race condition
send.c: move add_sllao code to its own function

This code is becoming a problem...isolate it so it can be tested.  This
also changes the code because len was not being correctly incremented.
send.c: move ensure_iface_setup to send.c

send.c is the only place this function is called, so ensure_iface_setup
should live there.
device-common.c: move check_ip6_forwarding here

check_ip6_forwarding was defined in radvd.c, but that's not a good place
for it to live.  It's better in device-common.c.

More function will eventually have to be migrated out of radvd.c, or at
lease the main function in radvd.c should be moved out to enable check
programs to link.
check: add check/sllao.c

Right now, this check is doing nothing but failing.  Fill in some code
later to make sure the new add_sllao is working correctly.
trivial.sh: run radvd longer (0.5s)

This test was running too quickly and not doing enough because of it.
syscalls_test.c: flesh out radvd_sendmsg a little
kickoff_adverts: schedule the iface even if send_ra_forall fails

I've seen the problem a few times.  Maybe send_ra_forall should go ahead
and reschedule the interface so the calling code doesn't have to.
remove syscalls.c and define the test calls as macros
declare add_sllao in radvd.h
do real testing in check/sllao.c