MDEV-452 Add full support for auto-initialized/updated timestamp and datetime

Generalized support for auto-updated and/or auto-initialized timestamp
and datetime columns. This patch is a reimplementation of MySQL's
"WL#5874: CURRENT_TIMESTAMP as DEFAULT for DATETIME columns". In order to
ease future merges, this implementation reused few function and variable
names from MySQL's patch, however the implementation is quite different.

TODO:
The only unresolved problem in this patch is the semantics of LOAD DATA for
TIMESTAMP and DATETIME columns in the cases when there are missing or NULL
columns. I couldn't fully comprehend the logic behind MySQL's behavior and
its relationship with their own documentation, so I left the results to be
more consistent with all other LOAD cases.

The problematic test cases can be seen by running the test file function_defaults,
and observing the test case differences. Those were left on purpose for discussion.

1 files changed, 1 insertions, 3 deletions

diff --git a/sql/sp_head.cc b/sql/sp_head.cc
index f3ba0073c69..11f962dd414 100644
--- a/sql/sp_head.cc
+++ b/sql/sp_head.cc
@@ -2426,7 +2426,6 @@ sp_head::fill_field_definition(THD *thd, LEX *lex,
 {
   LEX_STRING cmt = { 0, 0 };
   uint unused1= 0;
-  int unused2= 0;
 
   if (field_def->init(thd, (char*) "", field_type, lex->length, lex->dec,
                       lex->type, (Item*) 0, (Item*) 0, &cmt, 0,
@@ -2443,8 +2442,7 @@ sp_head::fill_field_definition(THD *thd, LEX *lex,
 
   sp_prepare_create_field(thd, field_def);
 
-  if (prepare_create_field(field_def, &unused1, &unused2, &unused2,
-                           HA_CAN_GEOMETRY))
+  if (prepare_create_field(field_def, &unused1, HA_CAN_GEOMETRY))
   {
     return TRUE;
   }