Observe passively interfaces created outside network manager.

Why:
The long standing woe of NM is it's inability to take not-yet-supported devices into account like bridges etc. The result is that in such cases, NM is either told not to interfere (NM_CONTROLLED=no in ifcfg-rh scripts) or outright disabled.

In first case, this behaviour leads to upper layer errors like apps thinking they're offline despite being online etc, in second case, it harms NM adoption.

Proposed fix:
1) Watch status of all network devices, no matter if they're being managed by NM or not
2) manage nm-managed devices using all available information (e.g.: eth0 is bridged into br0 and not nm-controlled, wlan0 is nm-controlled - NM should add default route to wlan0 if it is removed from br0 but once br0 comes back online, NM shouldn't "steal" default route from it)
3) report network availability to other programs based on such "complete picture" so that apps that rely on NM for network availability can learn that network is available albeit through non-nm-controlled interface

Notes:
this seems to me distinct to bug 589092 which is about honoring manual changes to NM-controlled interfaces.