* 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

apps/backend/backend_commit.c

@@ -518,8 +518,7 @@ validate_common(clicon_handle       h,
                  &td->td_tcvec,     /* changed: wanted values */
                  &td->td_clen) < 0)
         goto done;
-    if (clicon_debug_get()>1)
-        transaction_print(stderr, td);
+    transaction_dbg(h, CLIXON_DBG_DEFAULT, td, __FUNCTION__);
     /* Mark as changed in tree */
     for (i=0; i<td->td_dlen; i++){ /* Also down */
         xn = td->td_dvec[i];