Megacommit of many files.

Mostly, several functions that take pointers as arguments, almost
always char * pointers, had those pointers qualified with "const".
Those that returned pointers to previously const-qualified arguments
had their return values qualified as const.  Some structure members
were qualified as const to retain that attribute from the variables
from which they were assigned.

The macro DE_CONST was added to isc/util.h to deal with a handful of very
special places where something is qualified as const but really needs to have
its const qualifier removed.

Also cleaned up a few places where variable names clashed with reserved
identifiers.  (Which mostly works fine, but strictly speaking is undefined
by the standard.)

Minor other ISC style cleanups.

lib/isc/event.c

@@ -38,9 +38,10 @@ destroy(isc_event_t *event) {
 
 isc_event_t *
 isc_event_allocate(isc_mem_t *mctx, void *sender, isc_eventtype_t type,
-		   isc_taskaction_t action, void *arg, size_t size)
+		   isc_taskaction_t action, const void *arg, size_t size)
 {
 	isc_event_t *event;
+	void *deconst_arg;
 
 	if (size < sizeof (struct isc_event))
 		return (NULL);
@@ -50,8 +51,23 @@ isc_event_allocate(isc_mem_t *mctx, void *sender, isc_eventtype_t type,
 	event = isc_mem_get(mctx, size);
 	if (event == NULL)
 		return (NULL);
-	ISC_EVENT_INIT(event, size, 0, NULL, type, action, arg, sender,
-		       destroy, mctx);
+
+	/*
+	 * Removing the const attribute from "arg" is the best of two
+	 * evils here.  If the event->ev_arg member is made const, then
+	 * it affects a great many users of the task/event subsystem
+	 * which are not passing in an "arg" which starts its life as
+	 * const.  Changing isc_event_allocate() and isc_task_onshutdown()
+	 * to not have "arg" prototyped as const (which is quite legitimate,
+	 * because neither of those functions modify arg) can cause
+	 * compiler whining anytime someone does want to use a const
+	 * arg that they themselves never modify, such as with
+	 * gcc -Wwrite-strings and using a string "arg".
+	 */
+	DE_CONST(arg, deconst_arg);
+
+	ISC_EVENT_INIT(event, size, 0, NULL, type, action, deconst_arg,
+		       sender, destroy, mctx);
 
 	return (event);
 }