- fixes related to XATTRS status flag

XATTRS status flag is now placed on fixed (effectively reserved)
position no matter the ENABLE_XATTR #define state.
- make the xattributes comparison independent
  on File's status

We will compare xattributes each time without respect to
previous File's status. With certain exteded attributes
this will make the 'XAs have been modified' msg more
frequent as there're generaly different XAs for directories
and regular files (i.e.: SELinux, ACL). But this aproach
is closer to others attibutes concept at all.
- simplify operator<<(ostream, xa_value_t)
- do not test types matching in cmpFilesXattrs()
- simplify XAModification class

Remove map from XAModification class. This was left over
from time I thought it would be benefitial to have
the operations on xattribute ordered.