Bug#23068 - key_cache_block_size is not set or displayes correctly

Command line and configuration file option 'key_cache_block_size'
was reduced by MALLOC_OVERHEAD (8 in a production server, 36 in a
debug server) from the user supplied value and restricted it to
the greatest multiple of 512 less or equal to the reduced value.

This patch changes option 'key_cache_block_size' to not deduce
MALLOC_OVERHEAD from the input value. However, the restriction
to a multiple of 512 is still done.

sql/mysqld.cc

@@ -5806,7 +5806,7 @@ log and this option does nothing anymore.",
    (gptr*) &dflt_key_cache_var.param_block_size,
    (gptr*) 0,
    0, (GET_ULONG | GET_ASK_ADDR), REQUIRED_ARG,
-   KEY_CACHE_BLOCK_SIZE , 512, 1024*16, MALLOC_OVERHEAD, 512, 0},
+   KEY_CACHE_BLOCK_SIZE, 512, 1024 * 16, 0, 512, 0},
   {"key_cache_division_limit", OPT_KEY_CACHE_DIVISION_LIMIT,
    "The minimum percentage of warm blocks in key cache",
    (gptr*) &dflt_key_cache_var.param_division_limit,