config.h defines _GNU_SOURCE, which in turn defines the bits necessary
for kill, isblank, and isascii. So wherever we use those, we need
to make sure config.h is included.
When the client exits it may take a short amount of time for the
dhclient hook script to deliver the options to NetworkManager; so
we need to keep the client object around a bit (so we know what
NMDHCPClient the options getting delivered are for). If we don't,
the DHCPManager will dispose of the DHCPClient object and then
when the options come in, it can't match up the PID from the
options with the PID of an existing NMDHCPClient. So put the
clients on a removal timer that keeps them around for a bit before
we let the manager dispose of them.
Since we're keeping the PID around too instead of zeroing it when
the client exits (for the reason above), track whether the client
is really dead yet so we don't indiscriminately kill a random
process that happens to re-use the PID.
Clients in IPv6 info-only mode may exit after getting a response
from the server, since there are no leases involved in info-only
mode. To ensure that the client's options are received when the
event comes in (which could be after we get the child watch
callback for the exit) we still need the client's PID.
