Do not allow the m_transforming_liquid queue to increase until all RAM is consumed

minetest.conf.example

@@ -100,6 +100,9 @@
 #new_style_water = false
 # Max liquids processed per step
 #liquid_loop_max = 10000
+# The time (in seconds) that the liquids queue may grow beyond processing
+# capacity until an attempt is made to decrease its size by dumping old queue items
+#liquid_queue_purge_time = 30
 # Update liquids every .. recommend for finite: 0.2
 #liquid_update = 1.0
 # Enable nice leaves; disable for speed