bug#13454: 24.2; Small fix to reference manual

[Nathan Trapuzzano]

See attached patch for small fix to Emacs reference manual.

=== modified file 'doc/emacs/custom.texi'
--- doc/emacs/custom.texi       2012-06-11 06:48:47 +0000
+++ doc/emacs/custom.texi       2013-01-15 05:30:01 +0000
@@ -552,8 +552,8 @@
 between various collections of settings, and to transfer such
 collections from one computer to another.
 
-  A Custom theme is stored an Emacs Lisp source file.  If the name of
-the Custom theme is @var{name}, the theme file is named
+  A Custom theme is stored as an Emacs Lisp source file.  If the name
+of the Custom theme is @var{name}, the theme file is named
 @file{@var{name}-theme.el}.  @xref{Creating Custom Themes}, for the
 format of a theme file and how to make one.