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, 18 insertions, 0 deletions

diff --git a/sql/sql_string.cc b/sql/sql_string.cc
index 75029a03790..89536b93feb 100644
--- a/sql/sql_string.cc
+++ b/sql/sql_string.cc
@@ -502,6 +502,24 @@ bool String::append(IO_CACHE* file, uint32 arg_length)
   return FALSE;
 }
 
+
+/**
+  Append a parenthesized number to String.
+  Used in various pieces of SHOW related code.
+
+  @param nr     Number
+  @param radix  Radix, optional parameter, 10 by default.
+*/
+bool String::append_parenthesized(long nr, int radix)
+{
+  char buff[64], *end;
+  buff[0]= '(';
+  end= int10_to_str(nr, buff + 1, radix);
+  *end++ = ')';
+  return append(buff, (uint) (end - buff));
+}
+
+
 bool String::append_with_prefill(const char *s,uint32 arg_length,
 		 uint32 full_length, char fill_char)
 {