Use the InnoDB hash table for keeping track of INNOBASE_SHARE objects.

struct st_innobase_share: Make table_name const uchar*.  Add the member
table_name_hash.

innobase_open_tables: Change the type from HASH to hash_table_t*.

innobase_get_key(): Remove.

innobase_fold_name(): New function, for computing the fold value for the
InnoDB hash table.

get_share(), free_share(): Use the InnoDB hash functions.

innobase_end(): Free innobase_open_tables before shutting down InnoDB.
Shutting down InnoDB will invalidate all memory allocated via InnoDB.

rb://65 approved by Heikki Tuuri.  This addresses Issue #104.