adding preference option for dynamic input blocking

/inpblock is now having subcommands 'timeout' and 'dynamic'
with:

/inpblock timeout <milliseconds>

and

/inpblock dynamic <on|off>

Defaults are:

/inpblock timeout 500
/inpblock dynamic on

To get the old behavior specify:

/inpblock timeout 20
/inpblock dynamic off

The dynamic mode will block incrementally after something
should be written to the window or after a key was pressed. So pressing
a key would set the timeout to 0ms and after 10 timeouts to the next
bigger one.

Example (with dynamic mode on):

"/inpblock timeout 50"

timeout series:

10x 0ms
10x 10ms (0ms + 10 times since last keypress)
10x 30ms (10ms + 20 times since last keypress)
*x50ms until next key was pressed or

src/command/commands.c

@@ -3450,13 +3450,40 @@ cmd_notify(gchar **args, struct cmd_help_t help)
 gboolean
 cmd_inpblock(gchar **args, struct cmd_help_t help)
 {
-    char *value = args[0];
+    char *subcmd = args[0];
+    char *value = args[1];
     int intval;
-    if (_strtoi(value, &intval, 1, 1000) == 0) {
-        cons_show("Input blocking set to %d milliseconds.", intval);
-        prefs_set_inpblock(intval);
-        ui_input_nonblocking(FALSE);
+    if (strcmp(subcmd, "timeout") == 0) {
+        if (value == NULL) {
+            cons_show("Usage: %s", help.usage);
+            return TRUE;
+        }
+
+        if (_strtoi(value, &intval, 1, 1000) == 0) {
+            cons_show("Input blocking set to %d milliseconds.", intval);
+            prefs_set_inpblock(intval);
+            ui_input_nonblocking(FALSE);
+        }
+
+        return TRUE;
     }
+
+    if (strcmp(subcmd, "dynamic") == 0) {
+        if (value == NULL) {
+            cons_show("Usage: %s", help.usage);
+            return TRUE;
+        }
+
+        if (strcmp(value, "on") != 0 && strcmp(value, "off") != 0) {
+            cons_show("Dynamic must be one of 'on' or 'off'");
+            return TRUE;
+        }
+
+        return _cmd_set_boolean_preference(value, help, "Dynamic input blocking", PREF_INPBLOCK_DYNAMIC);
+    }
+
+    cons_show("Usage: %s", help.usage);
+
     return TRUE;
 }