udf: fix uid/gid permissions

udf: fix uid/gid permissions

This change made it into the 2.6 branch since 2.6.15 and fixes a problem
where the UDF code would change the ownership of files in a UDF filesystem
when they were different thatn the current user, when possible. Example: after
creating a CD using udf as a regular user, if you mounted the CD as root, the
udf code would reset the ownership of all the files on the cd, causing
unecessary write operations. I found this fix while working with an old patch
which adds packet-writing to the 2.4 kernel. This fix is from the original
author (or maintainer) of the udf code.

Note: this was fixed upstream in 4d6660eb3665f22d16aff466eb9d45df6102b254.