Add a RESTART (without parameter) option to ALTER SEQUENCE, allowing a

sequence to be reset to its original starting value.  This requires adding the
original start value to the set of parameters (columns) of a sequence object,
which is a user-visible change with potential compatibility implications;
it also forces initdb.

Also add hopefully-SQL-compatible RESTART/CONTINUE IDENTITY options to
TRUNCATE TABLE.  RESTART IDENTITY executes ALTER SEQUENCE RESTART for all
sequences "owned by" any of the truncated relations.  CONTINUE IDENTITY is
a no-op option.

Zoltan Boszormenyi