- ALTER_ALGORITHM should be substituted when there is no mention of
algorithm in alter statement.
- Introduced algorithm(thd) in Alter_info. It returns the
user requested algorithm. If user doesn't specify algorithm explicitly then
it returns alter_algorithm variable.
- changed algorithm() to get_algorithm(thd) to return algorithm name for
displaying the error.
- set_requested_algorithm(algo_value) to avoid direct assignment on
requested_algorithm variable.
- Avoid direct access of requested_algorithm to encapsulate
requested_algorithm variable
- Added the test case to prove that alter_algorithm variable doesn't
affect when ALTER statement during PREPARE PHASE or CREATE PROCEDURE.
Only when execution/call happens, alter uses the alter_algorithm
variable when user does not mention algorithm explicitly
