* NACM extension (RFC8341)

* NACM module support (RFC8341 A1+A2)
   * Recovery user "_nacm_recovery" added.
     * Example use is restconf PUT when NACM edit-config is permitted, then automatic commit and discard are permitted using recovery user.
   * Example user changed adm1 to andy to comply with RFC8341 example

 * Yang code upgrade (RFC7950)
   * RPC method input parameters validated
     * see https://github.com/clicon/clixon/issues/4
* Correct XML namespace handling
   * XML multiple modules was based on "loose" semantics so that yang modules were found by iterating thorugh namespaces until a match was made. This did not adhere to proper [XML namespace handling](https://www.w3.org/TR/2009/REC-xml-names-20091208), and causes problems with overlapping names and false positives. Below see XML accepted (but wrong), and correct namespace declaration:
```
      <rpc><my-own-method></rpc> # Wrong but accepted
      <rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"> # Correct
        <my-own-method xmlns="http://example.net/me/my-own/1.0">
      </rpc>
```
   * To keep old loose semantics set config option CLICON_XML_NS_ITERATE (true by default)
   * XML to JSON translator support for mapping xmlns attribute to module name prefix.
   * Default namespace is still "urn:ietf:params:xml:ns:netconf:base:1.0"
   * See https://github.com/clicon/clixon/issues/49
* Changed all make tags --> make TAGS
* Keyvalue datastore removed (it has been disabled since 3.3.3)
* debug rpc added in example application (should be in clixon-config).

test/test_leafref.sh

@@ -72,18 +72,19 @@ module example{
 }
 EOF
 
-# kill old backend (if any)
-new "kill old backend"
-sudo clixon_backend -zf $cfg -y $fyang
-if [ $? -ne 0 ]; then
-    err
-fi
+new "test params: -f $cfg -y $fyang"
 
-# start new backend
-new "start backend  -s init -f $cfg -y $fyang"
-sudo $clixon_backend -s init -f $cfg -y $fyang 
-if [ $? -ne 0 ]; then
-    err
+if [ $BE -ne 0 ]; then
+    new "kill old backend"
+    sudo clixon_backend -zf $cfg -y $fyang
+    if [ $? -ne 0 ]; then
+	err
+    fi
+    new "start backend  -s init -f $cfg -y $fyang"
+    sudo $clixon_backend -s init -f $cfg -y $fyang -D $DBG
+    if [ $? -ne 0 ]; then
+	err
+    fi
 fi
 
 new "leafref base config"
@@ -142,6 +143,10 @@ expectfn "$clixon_cli -1f $cfg -y $fyang -l o set sender a" 0 "^$"
 new "cli sender template"
 expectfn "$clixon_cli -1f $cfg -y $fyang -l o set sender b template a" 0 "^$"
 
+if [ $BE -ne 0 ]; then
+    exit # BE
+fi
+
 new "Kill backend"
 # Check if premature kill
 pid=`pgrep -u root -f clixon_backend`