COLUMN IN ALTER TABLE...ADD COLUMN

Analysis:
========

ISSUE1:
ALTER TABLE, INPLACE operation to add a DATE/DATETIME column fails
to report an error  when:
a) Field is NOT NULL and DEFAULT value is not supplied.
b) Strict and 'NO_ZERO_DATE' sql modes are enabled.
c) Table is not empty.

ISSUE2:
ALTER TABLE, INPLACE/COPY to add a DATE/DATETIME column fails with
an error:
a) Field is NOT NULL and DEFAULT value is not supplied.
b) Only strict mode is enabled.
c) Table is not empty.

The 'mysql_inplace_alter_table()' function did not handle the
condition mentioned in issue1 in order to report an error. A flag
'error_if_not_empty' is set  when the conditions mentioned in
issue1 occurs. This flag was not checked in
'mysql_inplace_alter_table()' to raise an error.

When only strict mode is enabled, the operation mentioned in
ISSUE2 is supposed to succeed. But 'mysql_prepare_alter_table',
checked for strict mode rather than 'NO_ZERO_DATE' when setting
the flag 'error_if_not_empty'. Thus the operation failed reporting
an error.

Fix:
===
ISSUE1: The 'mysql_inplace_alter_table()' is modified to check for the
        flag 'error_if_not_empty' and raise an error if the conditions
        mentioned in ISSUE1 occurs.
ISSUE2: 'mysql_prepare_alter_table()', has been modified to remove the
        check for strict mode while setting the 'error_if_not_empty'
        to report warning/error as appropriate.