(isearch-highlight): Set isearch-overlay priority to

(isearch-highlight): Set isearch-overlay priority to
1 here rather than each time through
isearch-lazy-highlight-new-loop.
(isearch-lazy-highlight-max): Variable deleted.
(isearch-lazy-highlight-max-at-a-time): New user variable, like
isearch-lazy-highlight-max but controls a single invocation of
isearch-lazy-highlight-update.
(isearch-lazy-highlight-wrapped): Variable recreated.
(isearch-lazy-highlight-window-start): New variable.
(isearch-lazy-highlight-cleanup): Restored to behavior of
before 2-Jan.
(isearch-lazy-highlight-remove-overlays): Function deleted;
behavior folded into isearch-lazy-highlight-cleanup.  "Keep"
behavior removed.
(isearch-lazy-highlight-new-loop): Restore old behavior of calling
isearch-lazy-highlight-update in a loop rather than just once.
Test isearch-invalid-regexp here and decide not to start a new
loop, rather than testing it each time through
isearch-lazy-highlight-update.
(isearch-lazy-highlight-search): Function restored.
(isearch-lazy-highlight-update): Get called in a timer loop again,
but this time highlight more than one match each time through.
Only highlight matches in the visible part of the window.  Start
at point, move in the direction of the search, and wrap around at
the edge of the window.  Use sit-for to force redisplay and ensure
window-start is credible.  "Face suppressing" behavior removed;
overlay priorities should make it unnecessary, right?
(isearch-highlight): Face suppressing behavior removed.
(isearch-dehighlight): Face suppressing behavior removed.
(isearch-set-lazy-highlight-faces-at): Removed.