Add DISCARD etc. in the keyword: rule of sql_yacc.yy
sql_table.cc:
  Add comment that DISCARD/IMPORT TABLESPACE is always the only clause in an ALTER TABLE


sql/sql_table.cc:
  Add comment that DISCARD/IMPORT TABLESPACE is always the only clause in an ALTER TABLE
sql/sql_yacc.yy:
  Add DISCARD etc. in the keyword: rule of sql_yacc.yy