Make isc_result a static enum

Remove the dynamic registration of result codes.  Convert isc_result_t
from unsigned + #defines into 32-bit enum type in grand unified
<isc/result.h> header.  Keep the existing values of the result codes
even at the expense of the description and identifier tables being
unnecessary large.

Additionally, add couple of:

    switch (result) {
    [...]
    default:
        break;
    }

statements where compiler now complains about missing enum values in the
switch statement.

lib/dns/validator.c

@@ -16,6 +16,7 @@
 #include <isc/md.h>
 #include <isc/mem.h>
 #include <isc/print.h>
+#include <isc/result.h>
 #include <isc/string.h>
 #include <isc/task.h>
 #include <isc/util.h>
@@ -36,7 +37,6 @@
 #include <dns/rdataset.h>
 #include <dns/rdatatype.h>
 #include <dns/resolver.h>
-#include <dns/result.h>
 #include <dns/validator.h>
 #include <dns/view.h>
 
@@ -568,7 +568,7 @@ fetch_callback_ds(isc_task_t *task, isc_event_t *event) {
 			 */
 			validator_log(val, ISC_LOG_DEBUG(3),
 				      "falling back to insecurity proof (%s)",
-				      dns_result_totext(eresult));
+				      isc_result_totext(eresult));
 			result = proveunsecure(val, false, false);
 			if (result != DNS_R_WAIT) {
 				validator_done(val, result);