Assorted tab-completion improvements in psql.

Assorted tab-completion improvements in psql.

Add missing completions for:
- ALTER SEQUENCE name OWNER TO
- ALTER TYPE name RENAME TO
- ALTER VIEW name ALTER COLUMN
- ALTER VIEW name OWNER TO
- ALTER VIEW name SET SCHEMA

Fix wrong completions for:
- ALTER FUNCTION/AGGREGATE name (arguments) ...
    "(arguments)" has been ignored.
- ALTER ... SET SCHEMA
    "SCHEMA" has been considered as a variable name.