Fix afs_AccessOK for dropbox case

Fix afs_AccessOK for dropbox case

afs_AccessOK did not check for if we have 'i' rights on a directory, nor
if we were the owner of a file, if we were only checking PRSFS_READ or
PRSFS_WRITE. Thus, it does not correctly address the 'dropbox'
permissions case (if you are the owner of a file and have insert
permissions, you get implicit 'r' and 'w').

Fix this to check for 'i' and ownership when we need to, so the dropbox
special-case check works as intended.

FIXES 126216

Change-Id: Ib629bc30b73bc3965e777747067259451f0adff6
Reviewed-on: http://gerrit.openafs.org/1143
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>