bug#18296: 24.4.50; doc string of `whitespace-mode'

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

1. Please mention which faces are used for which kinds of highlighting.

2. Wording:

 So, for example, if indentation and indentation::space are
 included in `whitespace-style' list, the indentation value is
 evaluated instead of indentation::space value.

 One reason for not visualize spaces via faces (if `face' is not
 included in `whitespace-style') is to use exclusively for
 cleaning up a buffer.  See `whitespace-cleanup' and
 `whitespace-cleanup-region' for documentation.

A minimal fix:

 For example, if `indentation' and `indentation::space' are included in
 `whitespace-style', the `indentation' value is used instead of the
 `indentation::space' value.

 One reason to not use faces to visualize spaces (i.e., not include
 `face' in `whitespace-style') is to use `whitespace-mode' only for
 cleaning up a buffer.  See `whitespace-cleanup' and
 `whitespace-cleanup-region'.


In GNU Emacs 24.4.50.1 (i686-pc-mingw32)
 of 2014-06-28 on ODIEONE
Bzr revision: 117431 rgm@gnu.org-20140628015517-eku6hj8mpgcvfnso
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/snapshot/trunk
 --enable-checking=yes,glyphs 'CFLAGS=-O0 -g3'
 LDFLAGS=-Lc:/Devel/emacs/lib 'CPPFLAGS=-DGC_MCHECK=1
 -Ic:/Devel/emacs/include''