[$] A farewell to set_fs()?

The archaeological evidence is murky, but it would appear that the kernel'sset_fs() function was added in November 1991 by a certain TedTs'o; it was in the 0.10 release. It is, thus, one of the oldest APIsfound within the kernel itself. Careless use of set_fs() hasalways been an easy way to create security bugs; a recent attempt to makethese bugs harder to exploit may instead result in this function being removedaltogether.