Added a test case for bug #6120.
sql_view.cc:
  Fixed bug #6120.
  The SP cache must be invalidated when a view is altered.


sql/sql_view.cc:
  Fixed bug #6120.
  The SP cache must be invalidated when a view is altered.
mysql-test/t/view.test:
  Added a test case for bug #6120.
mysql-test/r/view.result:
  Added a test case for bug #6120.