bug#2257: 23.0.90; grep-files-history has inappropriate default value

[Drew Adams]

emacs -Q
M-x load-library grep
C-h v grep-files-history
shows:
 
 grep-files-history is a variable defined in `grep.el'.
 Its value is ("ch" "el")
 Documentation:
 Not documented as a variable.
 
Besides the fact that there should be a doc string, the default value
should be nil.  `grep' already DTRT to fill the history with
appropriate default values for `M-n'. The default value of
`grep-files-history' is used only when no appropriate default values
are found.
 
And in that case, no default values should be available - it makes no
sense to propose inappropriate values. There is no reason for the
(first) default value to be proposed as [ch] in all cases - or in any
cases where a .c or .h file is not expected. Better for Emacs to
simply say that no default value is available.
 
 
 
In GNU Emacs 23.0.90.1 (i386-mingw-nt5.1.2600)
 of 2009-02-01 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'