Added attribute "extend_unbounded" at owner.

Until now, check for inconsistent extended owners was disabled globally.
This check should now be enabled globally with --check_owner_extend=1.
For individual owners, the check can be disabled again using
attribute "extend_unbounded".
Check has been improved and a test case was added.
Check for validity of attribute "show_all" has been fixed.
Added 'routing=dynamic', restrict 'routing=manual'

'routing=manual' is no longer allowed as attribute of interface, but
still at router. New 'routing=dynamic' has the same effect at interface
level. The new name shows more clearly, that the route isn't
configured manually but by some routing protocol.

The restriction of 'routing=manual' must be enabled by new config
option 'check_routing_manual'. This option will be removed in the next
but one release and the check will be fully enabled then.