Fix for Bug#35469: server crash with LOAD DATA INFILE to a VIEW.

The problem was that LOAD DATA code (sql_load.cc) didn't take into
account that there may be items, representing references to other
columns. This is a usual case in views. The crash happened because
Item_direct_view_ref was casted to Item_user_var_as_out_param,
which is not a base class.

The fix is to
  1) Handle references properly;
  2) Ensure that an item is treated as a user variable only when
     it is a user variable indeed;
  3) Report an error if LOAD DATA is used to load data into
     non-updatable column.


mysql-test/r/loaddata.result:
  Update result file.
mysql-test/t/loaddata.test:
  Add a test case form Bug#35469: server crash with
  LOAD DATA INFILE to a VIEW.
sql/share/errmsg.txt:
  Introduce a new error.
sql/sql_load.cc:
  Handle reference-items properly.
mysql-test/std_data/bug35649.data:
  Add a data file for the test case.

1 files changed, 3 insertions, 0 deletions

diff --git a/mysql-test/std_data/bug35649.data b/mysql-test/std_data/bug35649.data
new file mode 100644
index 00000000000..afcd9e9cc95
--- /dev/null
+++ b/mysql-test/std_data/bug35649.data
@@ -0,0 +1,3 @@
+"1", "string1"
+"2", "string2"
+"3", "string3"