* Changed debug levels in clicon_debug() to be based on maskable flags

* Added flag names: `CLIXON_DBG_*`
  * Added maskable flags that can be combined when debugging:
    * `DEFAULT` = 1: Basic debug message, espcially initialization
    * `MSG` = 2: Input and output packets, read datastore
    * `DETAIL` = 4: Details: message dump in hex, xpath parse trees, etc
    * `EXTRA` = 8: Extra detailed logs
* Test: some errors in yang-lib where content-id was in wrong place

test/test_netconf_monitoring_multiple.sh

@@ -55,9 +55,9 @@ EOF
 cat <<EOF > $dir/startup_db
 <${DATASTORE_TOP}>
   <yang-library xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library">
+     <content-id>42</content-id> <!-- XXX should be on yang-library level -->
      <module-set>
         <name>default</name>
-        <content-id>42</content-id>
         <module>
            <name>clixon-example</name>
            <revision>2000-01-01</revision>