+ *
+ * Needs cleaning! The way diff blocks are handled in append and reading is
+ * quite different, and likely to give maintenance problems.
+ *
+ * log levels (set isamd=x in zebra.cfg (or what ever cfg file you use) )
+ * 0 = no logging. Default
+ * 1 = no logging here. isamd logs overall statistics
+ * 2 = Each call to isamd_append with start address and no more
+ * 3 = Start and type of append, start of merge, and result of append
+ * 4 = Block allocations
+ * 5 = Block-level operations (read/write)
+ * 6 = Details about diff blocks etc.
+ * 7 = Log each record as it passes the system (once)
+ * 8 = Log raw and (de)coded data
+ * 9 = Anything else that may be useful
+ * .. = Anything needed toi hunt a specific bug
+ * (note that all tests in the code are like debug>3, which means 4 or above!)