revset: do not partial-match operator and function names in optimize() It was error-prone, and actually there was a typo, s/ancestorspec/ancestor/.

revset: remove false condition to process 'negate' operator 'negate' is mapped to 'string' at the above clause.

revset: make optimize() reject unknown operators This should have caught the bug of 'keyvalue' operator fixed at 5004ef47f437. The catch-all pattern is useless since optimize() should be aware of all known operators.

help: show content for explicitly disabled extension (issue5228)