change the return type of pool:close() to bool

Before the patch pool: close () return fixed "number" == 1.
This seems to mean "no errors". So let's use the same return
type as for the connection: close (). This will be more consistent.

Author: LeonidVas

mysql/init.lua

@@ -201,7 +201,7 @@ local function pool_close(self)
             mysql_conn:close()
         end
     end
-    return 1
+    return true
 end
 
 -- Returns connection