COLUMNS IN VIEWS

Issue:
charset value for a Column, returned by MYSQL_LIST_FIELDS(), was not same
for Table and View. This was because, for view, field charset was not being
returned.

Solution:
Added definition of function "charset_for_protocol()" in calss 
Item_ident_for_show to return field charset value.

sql/item.h:
  Added definition for charset_for_protocol() function to return field charset.
tests/mysql_client_test.c:
  Added a test case test_bug12337762 for the changes done.