Enforce 'rdev' (device file major/minor) is 0

Historically OSTree supported device files, but it wasn't useful, and
added attack surface.  Support was removed in

https://git.gnome.org/browse/ostree/commit/?id=62a896350bd54bff5a9413d2ee0fad7ff4364f9a

Perform a further cleanup by enforcing internally that the device
major/minor must be 0.

Conflicts:
	src/libostree/ostree-core.c

src/libostree/ostree-core-private.h

@@ -38,7 +38,7 @@ G_BEGIN_DECLS
  * u - uid
  * u - gid
  * u - mode
- * u - rdev
+ * u - rdev (must be 0)
  * s - symlink target 
  * a(ayay) - xattrs
  *
@@ -55,7 +55,7 @@ G_BEGIN_DECLS
  * u - uid
  * u - gid
  * u - mode
- * u - rdev
+ * u - rdev (must be 0)
  * s - symlink target 
  * a(ayay) - xattrs
  * ---