Post-merge fix: header is used by the client API. Obvious in retrospect.

Also, update a few cases missed by the initial patch.

client/mysqltest.cc:
  Remove trailing comma.
include/my_alloc.h:
  Do not use wrapper.
include/mysql.h.pp:
  Update ABI file.
plugin/semisync/semisync_master.h:
  Initialize variable.
sql/debug_sync.cc:
  Use C linkage.

include/my_alloc.h

@@ -23,7 +23,9 @@
 #define ALLOC_MAX_BLOCK_TO_DROP			4096
 #define ALLOC_MAX_BLOCK_USAGE_BEFORE_DROP	10
 
-C_MODE_START
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 typedef struct st_used_mem
 {				   /* struct for once_alloc (block) */
@@ -51,6 +53,8 @@ typedef struct st_mem_root
   void (*error_handler)(void);
 } MEM_ROOT;
 
-C_MODE_END
+#ifdef  __cplusplus
+}
+#endif
 
 #endif