bug#25776: 24.5; `imenu--generic-function' is not internal

[Drew Adams]

It is a relatively recent mania to name functions and variables using
`--' to indicate that they are internal.  This function should not be so
named.  It is referred to in several doc strings.  We do not (should
not) name functions specially just because we want to indicate that
users probably do not want to redefine them or that they are especially
likely to have their implementations changed in the future.  We don't
name `forward-char' `forward--char' just because it is (truly)
"internal".

Users exploring the doc strings of `imenu.el' encounter this function
name throughout.  Particularly if it is important to refer to the
function when documenting user-visible behavior, it makes little sense
to call it out as something "internal".

It is enough to add a comment in the code to suggest that users probably
do not want to mess with its definition or that its implementation is
especially likely to be changed in the future.

Each of these doc strings refers to `imenu--generic-function':

 imenu-generic-skip-comments-and-strings
 imenu-generic-expression
 imenu-syntax-alist
 imenu-default-create-index-function
 imenu-case-fold-search


In GNU Emacs 24.5.1 (i686-pc-mingw32)
 of 2015-04-11 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/usr --host=i686-pc-mingw32'