* Added valgrind memory leak tests in testmem.sh for restconf

* Added clicon_socket_set() and clicon_socket_get() functions for cleaning up backend server and restconf FCGI socket on termination.
* Removed obsolete `-x` command-line option to clixon_cli.

lib/src/clixon_handle.c

@@ -66,6 +66,17 @@
  * @note If you change here, you must also change the structs below:
  * @see struct cli_handle
  * @see struct backend_handle
+ * This is the internal definition of a "Clixon handle" which in its external
+ * form is "clicon_handle" and is used in most Clixon API calls.
+ * Some details:
+ * 1) the internal structure contains a header (defined here) whereas higher
+ *    order libs (eg cli and backend) introduce more fields appended to this 
+ *    struct.
+ * 2) ch_options accessed via clicon_data() are clixon config options are 
+ *    string values appearing in the XML configfile accessed with -f. 
+ *    Alternatively, these  could be accessed via clicon_conf_xml()
+ * 3) ch_data accessed via clicon_data() is more general purpose for any data.
+ *    that is, not only strings. And has separate namespace from options.
  */
 struct clicon_handle {
     int               ch_magic;    /* magic (HDR) */