libblkid: fix docs comment

Signed-off-by: Karel Zak <kzak@redhat.com>
build-sys: inform gtk-doc about __ul_attribute__

Signed-off-by: Karel Zak <kzak@redhat.com>
libblkid: clean up header file

 * don't teach people C by header files, so use warn_unused_result
   attribute only on places where we return allocated memory (to avoid
   leaks in applications).

Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: clean up header file

 * don't teach people C by header files, so use warn_unused_result
   attribute only on places where we return allocated memory (to avoid
   leaks in applications).

 * merge multiple function attributes to the one list to make it
   usable with gtk-doc

Signed-off-by: Karel Zak <kzak@redhat.com>
docs: update year

Signed-off-by: Karel Zak <kzak@redhat.com>