Warnings about rcs_id strings: let's settle this

[Alexander Kabaev]

> 
> only for const variables?  NO.  Many old codes do not declare the
> rcsid const, and the fact that we have the flag that will warn about
> all unused static variables means that users can still find them all.
>  
GCC 3.2 and prior only suppressed warnings for const variables. Since it
was the change from 3.2 to 3.3 which raised complaints, I guess adding
an option to restore 3.2 behavior is sufficient. Disabling warnings for
all static variables is going too far IMHO.

-- 
Alexander Kabaev