Fix some display-buffer related issues.

Fix some display-buffer related issues.

* window.el (enlarge-window, shrink-window): Don't mention return
value in doc-string (Bug#12896).
(window--display-buffer): Don't resize frames - it won't work
with all window managers and defeat pop-up-frame-alist.
(display-buffer-alist): In doc-string explain that CONDITION can
be a function and which arguments are passed to it (Bug#12854).
(display-buffer-assq-regexp): New argument ACTION.  Handle lambda
expressions (Bug#12854).
(display-buffer): Pass ACTION argument to
display-buffer-assq-regexp.

* windows.texi (Choosing Window): Rewrite description of
display-buffer-alist (Bug#12167).
(Display Action Functions): Mention inhibit-switch-frame.  Fix
description of display-buffer-below-selected.  Reorder actions.
Add example (Bug#12848).