DESC
remap_file_pages protection support: safety net for lazy arches
EDESC
From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

Since proper support requires that the arch at the very least handles
VM_FAULT_SIGSEGV, as in next patch (otherwise the arch may BUG), and things
are even more complex (see next patches), and it's triggerable only with
VM_NONUNIFORM vma's, simply refuse creating them if the arch doesn't declare
itself ready.

This is a very temporary hack, so I've clearly marked it as such. And, with
current rythms, I've given about 6 months for arches to get ready. Reducing
this time is perfectly ok for me.
