bug#10507: 24.0.92; Doc of `search-forward' (and backward)

[Drew Adams]

Both the doc in the Elisp manual and the doc string seem to be
incorrect, and this has apparently been the case for a very long time
(at least as far back as Emacs 20).
 
(search-forward "e" nil nil -1) searches BACKWARD for "e".
 
But the doc says that it searches FORWARD.
 
Furthermore, the doc says explicitly that the 4th arg MUST BE POSITIVE.
That is no only NOT the case, it is even the case that the Emacs lisp
code uses a negative value as the 4th arg.  See, e.g., `zap-to-char'.

In GNU Emacs 24.0.92.1 (i386-mingw-nt5.1.2600) of 2012-01-05 on MARVIN
 Windowing system distributor `Microsoft Corp.', version 5.1.2600
 configured using `configure --with-gcc (4.6) --no-opt --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include --ldflags
 -LD:/devel/emacs/libs/gnutls-3.0.9/lib'