When executing INSERT over a view with calculated columns it was assuming all
  elements of the fields collection are actually Item_field instances.
  This may not be true when inserting into a view and that view has columns that are 
  such expressions that allow updating (like setting a collation for example).
  Corrected to access field information through the filed_for_view_update() function and 
  retrieve correctly the field info even for "update-friendly" non-Item_field items.


mysql-test/r/view.result:
  Bug #21086: server crashes when VIEW defined with a SELECT with COLLATE clause is called
   - test suite
mysql-test/t/view.test:
  Bug #21086: server crashes when VIEW defined with a SELECT with COLLATE clause is called
   - test suite
sql/item_strfunc.h:
  Bug #21086: server crashes when VIEW defined with a SELECT with COLLATE clause is called
   - obvious typo fixed
sql/sql_base.cc:
  Bug #21086: server crashes when VIEW defined with a SELECT with COLLATE clause is called
   - must access field information through the filed_for_view_update() function to retrieve
     correctly the field info even for "update-friendly" non-Item_field items.