Add osv::run function

Add a convenience function, osv::run(), to run an ELF executable.

The patch includes extensive Doxygen documentation for the new function,
also detailing the how osv::run() differs from the familiar Linux
functions like exec(2).

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
mmu: VMA permission flags

Add permission flags to VMAs. They will be used by mprotect() and the
page fault handler.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
mmu: Anonymous memory demand paging

Switch to demand paging for anonymous virtual memory.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
tst-mmap.so: mincore() tests for demand paging

As suggested by Nadav, add tests for mincore() interraction with demand
paging.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>