Clean up the mess from => patch.

Commit 865f14a2 was quite a few bricks
shy of a load: psql, ecpg, and plpgsql were all left out-of-step with
the core lexer.  Of these only the last was likely to be a fatal
problem; but still, a minimal amount of grepping, or even just reading
the comments adjacent to the places that were changed, would have found
the other places that needed to be changed.