putenv/setenv changes

[Alan Barrett <apb%cequrux.com@localhost>]

On Sat, 02 Oct 2010, Matthias Scheler wrote:
> Modified Files:
>       src/lib/libc/stdlib: putenv.c setenv.c
> 
> Log Message:
> Restore binary compatibility with application which use putenv(3) on
> contant strings (e.g. postdrop(1)):
> - Don't write to the environment string passed to putenv(3).
> - Don't overwrite the value of an existing in setenv(3) unless the memory
>   was actually allocated by setenv(3).

Please document this.

I suggest a BUGS section in putenv(3) stating that that the interface
uses non-const char* for compatibility with POSIX brain damage, but the
implementation guarantees to treat it as read-only.

--apb (Alan Barrett)