change sm->new_block() to return an optional

space_map_recursive.cc

@@ -85,14 +85,21 @@ namespace {
 			}
 		}
 
-		virtual block_address new_block() {
-			// new_block can recurse, because we know it's
-			// looking up entries in the _previous_
-			// transaction.
+		// new_block must not recurse.
+		virtual boost::optional<block_address>
+		new_block() {
+			cant_recurse("new_block");
 			recursing_lock lock(*this);
 			return sm_->new_block();
 		}
 
+		virtual boost::optional<block_address>
+		new_block(block_address begin, block_address end) {
+			cant_recurse("new_block(range)");
+			recursing_lock lock(*this);
+			return sm_->new_block(begin, end);
+		}
+
 		virtual bool count_possibly_greater_than_one(block_address b) const {
 			if (depth_)
 				return true;