Previous patch (5a1e1aac) tried to minimize the amount of
open()s called when mmap()ing the files. Unfortunatley, there
was a mistake and wrong flags were compared which resulted in
the whole optimization working randomly (typically not
working).

Fixing the flags comparison revealed another problem. The
patch in question correllated with the 03e8c417 one, which
caused some vmas to be opened and mmaped much later than the
premap. When hitting the situation when vmas sharing their
fds are partially premapped and partially not, the whole
vm_open sharing became broken in multiple places -- either
needed fd was not opened, or the not needed left un-closed.

To fix this the context, that tracks whether the fd should
be shared or not, should be moved from collect stage to
the real opening loop. In this case we need to explicitly
know which vmas _may_ share fds (file private and shared)
with each other, so the sharing knowledge becomes spread
between open_filemap() and its callers. Oh, well...
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>