bug#22018: 25.0.50; REGRESSION wrt `isearch-new-word'

[Drew Adams <drew.adams@oracle.com>]

You essentially did a global replace of `isearch-word' and
`isearch-new-word' with `isearch-regexp-function' and
`isearch-new-regexp-function'.

You provided a `define-obsolete-variable-alias' for `isearch-word',
which is a global variable.  But you did nothing to accommodate
`isearch-new-word'.

This incompatible change breaks existing code that was promised that it
could set `isearch-new-word' in order to affect the subsequent behavior
(of `isearch-word', now renamed to `isearch-regexp-function').

A user or existing code needs to continue to be able to set
`isearch-new-word' OR `isearch-new-regexp-function'.  If
`isearch-new-word' is bound then `isearch-new-regexp-function' should be
set to its value, so that `isearch-regexp-function' will be properly
updated.

(setq ...
      isearch-regexp-function  (if (boundp 'isearch-new-word)
                                   isearch-new-word
                                 isearch-new-regexp-function)
      ...)

In GNU Emacs 25.0.50.1 (i686-pc-mingw32)
 of 2015-11-12
Bzr revision: 6e5186e8a7ccfb9b8fb35b5f4f0371e4f4a68162
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/snapshot/trunk
 --enable-checking=yes,glyphs --enable-check-lisp-object-type
 --without-compress-install --with-wide-int 'CFLAGS=-O0 -ggdb3'
 LDFLAGS=-Lc:/Devel/emacs/lib 'CPPFLAGS=-DGC_MCHECK=1
 -Ic:/Devel/emacs/include''