make lxc-checkconfig more explicit

make lxc-checkconfig more explicit

With a friend, we installed lxc on his server.
We spend 1 hour on the kernel config because we didn't knew :
- that lxc-checkconfig is a bash script and it can check a config before
running it
- which kernel config item whas not good
- that CONFIG_SECURITY_FILE_CAPABILITIES is obsolete since 2.6.33

So, here is a patch for lxc-checkconfig that could save time for lxc newbies

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Modified-by: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Guillaume Zitta <lxc@zitta.fr>