kernel: add magic option which makes ext4 usable

closes #101
kernel: enable security flags which make setcap usable

closes #102
write-hd-image.sh: use ext4 for rootfs
add "ping-perms" package for enabling cap_net_raw on ping binary

closes #93
finalizes #32
core: add su and ping-perms
add posix-man to core
*-man: depend on less

since we tuned busybox' man to use less -s to display man pages,
we need the less package as well since bb doesnt implement the -s
switch:

-s or --squeeze-blank-lines
Causes consecutive blank lines to be squeezed into a single blank line.
This is useful when viewing nroff output.