Support of views wasn't implemented for the TRUNCATE statement.
Now TRUNCATE on views has the same semantics as DELETE FROM view:
mysql_truncate() checks whether the table is a view and falls back
to delete if so.
In order to initialize properly the LEX::updatable for a view
st_lex::can_use_merged() now allows usage of merged views for the
TRUNCATE statement.


mysql-test/r/truncate.result:
  Added a test case for the Bug#5507: TRUNCATE does not work with views.
mysql-test/t/truncate.test:
  Added a test case for the Bug#5507: TRUNCATE does not work with views.
sql/sql_lex.cc:
  Bug#5507: TRUNCATE does not work with views.
  can_use_merged() was denying of usage of merged views for a
  TRUNCATE statement. This results in improper initialization
  of view LEX::updatable. Fixed.
sql/sql_delete.cc:
  Bug#5507: TRUNCATE does not work with views.
  1.mysql_truncate() was lacking of check whether the table is view. Added.
  2.mysql_truncate() calls mysql_delete(), but mysql_delete() always reports
  errors as "DELETE" errors. Fixed.
mysql-test/t/view.test:
  Updated test case for Bug#14540: OPTIMIZE, ANALYZE, REPAIR applied 
  to not a view.
mysql-test/r/view.result:
  Updated test case for Bug#14540: OPTIMIZE, ANALYZE, REPAIR applied 
  to not a view.