Add support for garbage collecting info passed to the plugin before

exit to appease address sanitizer's leak detector (and valgrind's
leak checker).  We can't free these sooner since the plugin may be
using the memory.  For plugin API 2.0 it should be make clear that
the plugin must make a copy of the data in the arrays passed in to
the plugin's open() function.  Only enabled if NO_LEAKS is defined.

src/sudo_plugin_int.h

@@ -87,7 +87,7 @@ struct plugin_container {
     TAILQ_ENTRY(plugin_container) entries;
     struct sudo_conf_debug_file_list *debug_files;
     const char *name;
-    const char *path;
+    char *path;
     char * const *options;
     void *handle;
     int debug_instance;