Addresses #2042 refs[t:2042] Fix race condition at lower level.

git-svn-id: file:///svn/toku/tokudb@14802 c7de825b-a66e-492c-adef-691d508d4ae1

newbrt/checkpoint.c

@@ -143,8 +143,10 @@ toku_multi_operation_client_unlock(void) {
 
 void 
 toku_checkpoint_safe_client_lock(void) {
+    toku_multi_operation_client_lock();
     int r = toku_pthread_rwlock_rdlock(&checkpoint_safe_lock);   
     assert(r == 0);
+    toku_multi_operation_client_unlock();
 }
 
 void