Handle L0 cache being full

A test thta will cause leveled to crash due to a low cache size being set - but protect against this (as well as the general scenario of the cache being full).

There could be a potential case where a L0 file present (post pending) without work backlog being set.  In this case we want to roll the level zero to memory, but don't accept the cache update if the L0 cache is already full.

src/leveled_log.erl

@@ -139,7 +139,7 @@
         {warn, "We're doomed - intention recorded to destroy all files"}},
     {"P0031",
         {info, "Completion of update to levelzero"
-                    ++ " with cache size status ~w ~w"}},
+                    ++ " with cache_size=~w status=~w and update_success=~w"}},
     {"P0032",
         {info, "Fetch head timing with sample_count=~w and level timings of"
                     ++ " foundmem_time=~w found0_time=~w found1_time=~w" 
@@ -171,6 +171,8 @@
         {info, "Archiving filename ~s as unused at startup"}},
     {"P0041",
         {info, "Penciller manifest switched from SQN ~w to ~w"}},
+    {"P0042",
+        {warn, "Cache full so attempting roll memory with l0_size=~w"}},
         
     {"PC001",
         {info, "Penciller's clerk ~w started with owner ~w"}},