client: moved ifdown,ifcheck to separate files
client: updated copyright and license statements
client: consider config in ifstatus, exit code rework

Moved ifstatus to separate files, changed to use fsm to
consider current config files and refactored to split the
status checks using new ifcheck helpers from showing info.

Reworked "ifstatus all" to reduce the status to well-known
LSB 0..4 codes considering mandatory devices and consistent
use of >150 codes [LSB app range] in a single interface run.
Adpted the ifup compat and systemv network init scripts.
Merge pull request #134 from mtomaschewski/ifstatus

client: consider config in ifstatus, exit code rework, copyright/license updates