[jcifs] New method in SmbFile

[Juan Gregorio de las Heras]

Hello,

For my project I need the user and group owner of a file. I have extended the
SmbFile with tow new methods to find the SID.  If you find this changes useful
to incorporate to the code, you can do it freely. I can't send the patch
included in the form because it considers me "top-posting". Can I send the patch
in other form.

Thank you