Change the name of the analyze_as_needed pragma to "optimize". Enhance the

Change the name of the analyze_as_needed pragma to "optimize".  Enhance the
comment (which will become documentation, assuming these changes land on trunk)
to explain that the optimize pragma is likely to be enhanced in various ways
in future releases and that applications should not depend upon the current
behavior.

FossilOrigin-Name: 9fced545a6f80c55d6dc4a6106cb2d3569566b3e