Refuse to load app_voicemail if res_adsi is not loaded (which is a symbol dependency)

(closes issue #11760)
 Reported by: non-poster
 Patches: 
       20080114__bug11760.diff.txt uploaded by Corydon76 (license 14)
 Tested by: Corydon76, non-poster, jamesgolovich


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@103556 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_voicemail.c

@@ -7903,6 +7903,13 @@ static int unload_module(void)
 static int load_module(void)
 {
 	int res;
+	char *adsi_loaded = ast_module_helper("", "res_adsi.so", 0, 0, 0, 0);
+	free(adsi_loaded);
+	if (!adsi_loaded) {
+		ast_log(LOG_ERROR, "app_voicemail.so depends upon res_adsi.so");
+		return AST_MODULE_LOAD_DECLINE;
+	}
+
 	my_umask = umask(0);
 	umask(my_umask);
 	res = ast_register_application(app, vm_exec, synopsis_vm, descrip_vm);