DESC
remap_file_pages protection support: VM_FAULT_SIGSEGV permission checking rework
EDESC
From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

Simplify the generic arch permission checking: the previous one was clumsy, as
it didn't account arch-specific implications (read implies exec, write implies
read, and so on).

Still to undo fixes for the archs (i386 and UML) which were modified for the
previous scheme.
