Add some new API to NMConfig so that NMSettings and its plugins can
use NMConfig to look up values rather than reparsing the config file
themselves.
Also, move the no-auto-default cache from NetworkManager.conf to
$NMSTATEDIR/no-auto-default.state, so NM isn't rewriting its own
config file at runtime.
Can't leave the backup files lying around when doing 'make distcheck',
so when backup up a file, return the backup file path so that the
caller can (optionally) remove it.
Finding out interface type from interface name string is fragile. It is easily
broken, e.g. by biosdevname changing interface names to em<n> or p<n>*p<n>.
Sadly, Gentoo network configuration scripts are rather stupid, using format:
variable_${interface|mac|essid|apmac}.
http://www.gentoo.org/doc/en/handbook/2007.0/handbook-x86.xml?full=1#book_part4_chap2
The entries interface|mac|essid|apmac are basically indistinguishable. It's not
possible to say whether 'p1p1' is an interface or SSID, for example.
Fix the current behaviour a bit by checking whether the string is an interface.
If so, and it is not a Wi-Fi one, set the connection type as wired. Else it is
regarded as wireless.
