Split item->flags into base_flags and with_flags

This was done to simplify copying of with_* flags

Other things:
- Changed Flags to C++ enums, which enables gdb to print
  out bit values for the flags. This also enables compiler
  errors if one tries to manipulate a non existing bit in
  a variable.
- Added set_maybe_null() as a shortcut as setting the
  MAYBE_NULL flags was used in a LOT of places.
- Renamed PARAM flag to SP_VAR to ensure it's not confused with persistent
  statement parameters.

1 files changed, 2 insertions, 2 deletions

diff --git a/sql/item_xmlfunc.h b/sql/item_xmlfunc.h
index 3369304d79c..1d2b6e70995 100644
--- a/sql/item_xmlfunc.h
+++ b/sql/item_xmlfunc.h
@@ -110,12 +110,12 @@ protected:
 public:
   Item_xml_str_func(THD *thd, Item *a, Item *b): Item_str_func(thd, a, b)
   {
-    flags|= ITEM_FLAG_MAYBE_NULL;
+    set_maybe_null();
   }
   Item_xml_str_func(THD *thd, Item *a, Item *b, Item *c):
     Item_str_func(thd, a, b, c)
   {
-    flags|= ITEM_FLAG_MAYBE_NULL;
+    set_maybe_null();
   }
   bool fix_fields(THD *thd, Item **ref);
   bool fix_length_and_dec();