sync: implement a somewhat serious LRU cache for the patch list value function; what was there before was broken and slow
sync: implement a somewhat serious LRU cache for the patch list value function; what was there before was broken and slow

tscholl2/smc,sagemathinc/smc,DrXyzzy/smc,tscholl2/smc,DrXyzzy/smc,sagemathinc/smc,tscholl2/smc,tscholl2/smc,tscholl2/smc,sagemathinc/smc,DrXyzzy/smc,DrXyzzy/smc,sagemathinc/smc