Patch for unix extensions

[Steven French]

>This is a small patch which added a new config option to turn the
>ensure_link_is_safe check off.

The link check for symlinks also incorrectly parses relative target paths
as relative to the root of the share name rather than relative to the
directory containing the symbolic link file.    So a link of a file
dir1/foo1 to ../dir1/foo2  would actually fail even though they are both
within the same share (and in the same directory).   This is one of the few
areas where the cifs vfs can not easily emulate Unix semantics to Samba
(although I am experimenting with an alternate approach using reparse
points that might work).

Steve French
Senior Software Engineer
Linux Technology Center - IBM Austin
phone: 512-838-2294
email: sfrench at us.ibm.com