FOR REFUSING OPERATION

The problem was that an ALTER TABLE statement using a LOCK/ALGORITHM
value not supported for the given operation(s), only gave a very generic
error message "This version of MySQL doesn't yet support ..."

This patch improves on the situation by giving a more detailed error
message - listing what is not supported, optionally explaining why,
and suggesting an alternative. For example: "LOCK=NONE is not supported.
Reason: COPY algorithm requires at least SHARED lock. Try LOCK=SHARED."

Since generally only the storage engine knows why a specific operation
is not supported, the handler interface is extended by adding
Alter_inplace_info::unsupported_reason. This allows the storage engine
to specify a detailed reason. If this field is set, the error message
reported is "%s is not supported. Reason: %s Try %s.". Otherwise the more
generic "%s is not supported for this operation. Try %s." is used.