Implemented a new INFORMATION_SCHEMA table, which is intended to
provide information about tablespaces.

mysql-test/r/information_schema.result:
  Updated test result according to WL#2511. With this WL
  I_S has new TABLESPACES schema.
mysql-test/r/information_schema_db.result:
  Updated test result according to WL#2511. With this WL
  I_S has new TABLESPACES schema.
mysql-test/r/mysqlshow.result:
  Updated test result according to WL#2511. With this WL
  I_S has new TABLESPACES schema.
mysql-test/suite/funcs_1/r/is_columns_is.result:
  Updated test result according to WL#2511. With this WL
  I_S has new TABLESPACES schema.
mysql-test/suite/funcs_1/r/is_tables_is.result:
  Updated test result according to WL#2511. With this WL
  I_S has new TABLESPACES schema.
sql/handler.h:
  Added SCH_TABLESPACES to enum_schema_tables.
sql/mysql_priv.h:
  Added human readable definitions for I_S.TABLESPACES field
  identifiers.
sql/sql_show.cc:
  Added I_S.TABLESPACES schema. The code which handles I_S.FILES
  is capable to handle I_S.TABLESPACES as well. Thus we reuse
  this code and let functions/variables have more generic names.