Change cache.c assert logic based on Hallvard's suggestion.

"Check that the entry has no writers before removing it from the
  cache" sounds more sensible to me than "check that it *has* writers"
  before removing it.
I've also changed the default cachesize for tests to 4.  This
should help discover such problems.

servers/slapd/back-ldbm/cache.c

@@ -200,7 +200,7 @@ cache_add_entry_lock(
 
 			/* XXX check for writer lock - should also check no readers pending */
 #ifdef LDAP_DEBUG
-			assert(pthread_rdwr_wchk_np(&e->e_rdwr));
+			assert(!pthread_rdwr_rwchk_np(&e->e_rdwr));
 #endif
 
 			/* delete from cache and lru q */

tests/data/slapd-master.conf

@@ -10,6 +10,7 @@ schemacheck	off
 #######################################################################
 
 database	ldbm
+cachesize	4
 suffix		"o=University of Michigan, c=US"
 directory	./test-db
 rootdn		"cn=Manager, o=University of Michigan, c=US"