CONFIG_SITE format change

[Ilya N. Golubev]

Version: 2.61 or earlier.

`CONFIG_SITE' value format changed incompatibly.  Previously it was a
list of file names.  This was reasonable at least in that if this
variable is not set, `configure' tries to load several files in order,
and it takes specifying a list of files to repeat this behavior by
setting `CONFIG_SITE'.  (There may be the same reasons not to use
`unset' as are in autoconf itself.)  Now `$CONFIG_SITE' is single file
name.  The default behavior can not be repeated by setting its value.

Did use several files in `$CONFIG_SITE' in other ways.  Keeping its
settings structured into these files certainly makes sense.

Worse, this user visible incompatible change is not even described in
`NEWS'.  Let alone any reasons are stated to impair user capabilities
this way.

Certainly can work around this by writing single file trying to load
other ones.  And it is tedious and error prone at best, and most
likely just duplicates the code / functionality that previously was in
autoconf core.

Please decide should this new behavior be retained in the first place,
or something else should be done.  Perhaps it is just reverting to the
old behavior.  Perhaps it is defining quite different conventions to
do equivalent things, that allow specifying lists of files, but less
prone to errors like those that inevitably occur if try to use
arbitrary value of any shell variable as list of something.

Anyway, please note what is decided in `NEWS'.