Fix for BUG#2477 "Slave stop with error after master reboot if use HEAP tables":

when we open the HEAP table for the first time since server restart,
in hp_open(), we set a flag to propagate this info to the handler level
which then writes a DELETE FROM this_heap_table to the binlog.
It is not a perfect solution for the bug, because between the server start and 
the first open of the table, the slave still had old data in his table so
a SELECT on the slave may show wrong content. But if there is a --init-file
to populate the HEAP table on master as startup, then this is a safe fix
(I'll put a note about init-file in the HEAP section of the manual).


heap/hp_info.c:
  new info variable implicit_emptied
heap/hp_open.c:
  If this is the first open of the HEAP table, it means it is empty,
  so we mark it.
include/heap.h:
  new variables implicit_emptied
  (we need one in HEAPINFO for the hp_info() call).
sql/ha_heap.cc:
  report info to upper level
sql/handler.h:
  new info 'implicit_emptied' in the handler level; only HEAP uses it.
sql/sql_base.cc:
  When a HEAP table is opened for the first time, write a DELETE FROM to the binlog,
  for replication and mysqlbinlog|mysql.
  Monty: I added the
  entry->file->implicit_emptied= 0;

include/heap.h

@@ -47,6 +47,7 @@ typedef struct st_heapinfo		/* Struct from heap_info */
   ulong index_length;
   uint reclength;			/* Length of one record */
   int errkey;
+  my_bool implicit_emptied;
 } HEAPINFO;
 
 
@@ -126,6 +127,7 @@ typedef struct st_heap_info
   int  mode;				/* Mode of file (READONLY..) */
   uint opt_flag,update;
   byte *lastkey;			/* Last used key with rkey */
+  my_bool implicit_emptied;
 #ifdef THREAD
   THR_LOCK_DATA lock;
 #endif