memcachetest aborts on textual get SERVER_ERROR

Now that moxi responds with SERVER_ERROR instead of END for a membase bucket type when a node is down, memcachetest aborts.

(Perhaps this END vs SERVER_ERROR vs just-close-the-connection needs a rethink. But that's another day.)

Here's a quick fix...

diff --git a/libmemc.c b/libmemc.c
index f734a97..cc9af37 100644
— a/libmemc.c
+++ b/libmemc.c
@@ -743,6 +743,8 @@ static int textual_get(struct Server* server, struct Item* i
return 0;
} else if (strstr(server->buffer, "END") == server->buffer)

else if (strstr(server->buffer, "SERVER_ERROR") == server->buffer)

abort();