bug#10550: 24.0.92; doc of `history-length'

[Drew Adams]

First, this var should really have `max' in its name.
As a general rule, numeric limit vars should have `max' or
`min' in the name.
 
As far as the doc goes, the most important thing is missing.  One can
pretty much guess that this value limits the length of history lists,
but the question is which history-list entries are dropped: the oldest
or the new ones?  Does the list stay the same, with new values rejected,
or do new ones replace the oldest ones? Or do new ones replace the
next-newest ones?  Why make users guess or experiment?
 
And for the doc string the info is also missing about which history
lists are affected: "those that don't specify their own maximum lengths"
(to quote the Elisp manual).
 

In GNU Emacs 24.0.92.1 (i386-mingw-nt5.1.2600) of 2012-01-16 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'