The change_to_use_tmp_fields function leaves the orig_table member of an
expression's tmp table field filled for the new Item_field being created.
Later orig_table is used by the Field::make_field function to provide some
info about original table and field name to a user. This is ok for a field
but for an expression it should be empty.

The change_to_use_tmp_fields function now resets orig_table member of
an expression's tmp table field to prevent providing a wrong info to a user.
The Field::make_field function now resets the table_name and the org_col_name
variables when the orig_table is set to 0.


sql/field.cc:
  Bug#27990: Wrong info in MYSQL_FIELD struct members when a tmp table was used.
  The Field::make_field function now resets the table_name and the org_col_name
  variables when the orig_table is set to 0.
sql/sql_select.cc:
  Bug#27990: Wrong info in MYSQL_FIELD struct members when a tmp table was used.
  The change_to_use_tmp_fields function now resets orig_table member of
  an expression's tmp table field to prevent providing a wrong info to a user.
tests/mysql_client_test.c:
  The test case for the bug#21635 is altered to test behavior on both const and
  non-const tables.