Many InnoDB internal variables and counters were only exposed
in an unstructured fashion via SHOW ENGINE INNODB STATUS.

Expose more variables via SHOW STATUS. Many of these were
exported in XtraDB.

Also, introduce SHOW_SIZE_T and use the proper size for
exporting the InnoDB variables.

Remove some unnecessary indirection via export_vars, and
bind some variables directly.

dict_sys_t::rough_size(): Replaces dict_sys_get_size()
and includes the hash table sizes.

This is based on a contribution by Tony Liu from ServiceNow.