vis: process aliased key sequences individually

While the complete alias is added to the input queue,
the called key bindings should only see the keys they
have asked for.

Previously a mapping such as:

 :map! normal gv \"^Sv

did not work as expected because the key binding for
the register did reject an invalid multi letter register
name.

Might also influence martanne#581

vis.c

@@ -1185,12 +1185,22 @@ static void vis_keys_process(Vis *vis, size_t pos) {
 				strcpy(vis->key_prev, vis->key_current);
 				strncpy(vis->key_current, start, len);
 				vis->key_current[len] = '\0';
-				end = (char*)binding->action->func(vis, binding_end, &binding->action->arg);
+				char *params_end = binding_end;
+				while (params_end) {
+					tmp = *params_end;
+					*params_end = '\0';
+					end = (char*)binding->action->func(vis, binding_end, &binding->action->arg);
+					*params_end = tmp;
+					if (end) {
+						start = cur = end;
+						break;
+					}
+					params_end = (char*)vis_keys_next(vis, params_end);
+				}
 				if (!end) {
 					end = start;
 					break;
 				}
-				start = cur = end;
 			} else if (binding->alias) {
 				buffer_remove(buf, start - buf->data, binding_end - start);
 				buffer_insert0(buf, start - buf->data, binding->alias);