bug#30978: 25.3; Suggestion: define-minor-mode should define mode-lighter variable

[Howard Melman]

Some packages define a user option to let users configure
the lighter string used in the mode-line, but some just use
a hard coded string. Packages such as diminish, delight and
dim exist to help customize these.

The define-minor-mode macro creates keymaps and other things
to help mode authors follow conventions. If it created a
mode-lighter user option when passed in a string (and not a
symbol) then users would have an easier time configuring
their mode-line without having to find and install a package
to do so.

Howard

In GNU Emacs 25.3.3 (x86_64-apple-darwin13.4.0, Carbon Version 157 AppKit 
1265.21)
of 2017-09-28 built on Atago.local