Static disabled plugins|engines and dynamic plugins which installed but disabled
are not visible in I_S PLUGINS|ENGINES tables because they are not stored into
global plugin array.
The fix: add such plugins|engines to plugin array with PLUGIN_IS_DISABLED status.
I_S.ENGINES 'Transactions', 'XA', 'Savepoints' fields have NULL value in this case.


mysql-test/r/warnings_engine_disabled.result:
  test result
mysql-test/suite/funcs_1/r/is_columns_is.result:
  result fix
mysql-test/suite/funcs_1/r/is_engines.result:
  result fix
mysql-test/t/warnings_engine_disabled.test:
  test case
sql/sql_plugin.cc:
  store disabled plugins|engines into plugin array
sql/sql_plugin.h:
  added PLUGIN_IS_DISABLED flag
sql/sql_show.cc:
  added filling of 'engines'&'plugins' tables with disabled engines|plugins