Declaring an all space column name in the SELECT FROM DUAL or in a view
leads to misleading warning message:
"Leading spaces are removed from name ' '".

The Item::set_name method has been modified to raise warnings like
"Name ' ' has become ''" in case of the truncation of an all
space identifier to an empty string identifier instead of the
"Leading spaces are removed from name ' '" warning message.


sql/item.cc:
  Fixed bug #27695.
  The Item::set_name method has been modified to raise warnings like
  "Name ' ' has become ''" in case of the truncation of an all
  space identifier to an empty string identifier instead of the
  "Leading spaces are removed from name ' '" warning message.
sql/share/errmsg.txt:
  Fixed bug #27695.
mysql-test/t/select.test:
  Added test case for bug #27695.
mysql-test/r/select.result:
  Added test case for bug #27695.