telldir()/seekdir() portability fixes

POSIX says that an offset obtained from telldir() can only be used
on the same DIR *. Linux is abls to reuse the offset accross
closedir()/opendir() for a given directory, but this is not portable
and such a behavior should be fixed.

An incomplete fix for the posix xlator was merged in
http://review.gluster.org/8933
This change set completes it.

- Perform the same fix index xlator.
- Use appropriate casts and variable types so that 32 bit signed
  offsets obtained by telldir() do not get clobbered when copied into
  64 bit signed types.
- modify afr-self-heald.c so that it does not use anonymous fd,
  since this will cause closedir()/opendir() between each
  syncop_readdir(). On failure we fallback to anonymous fs
  only for Linux so that we can cope with updated client vs not
  updated brick.
- Avoid sending an EINVAL when the client request for the EOF offset.
  Here we fix an error in previous fix for posix xlator: since we
  fill each directory entry with the offset of the next entry, we
  must consider as EOF the offset of the last entry, and not the
  value of telldir() after we read it.

This is a backport of I59fb7f06a872c4f98987105792d648141c258c6a

BUG: 1138897
Change-Id: I1e9f3e4a7d780b98adf6d9f197ee2198d43ef94d
Signed-off-by: Emmanuel Dreyfus <manu@netbsd.org>
Reviewed-on: http://review.gluster.org/9084
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>