[Patch 988444]

[Patch 988444]
Read multiple special headers
- fixed/improved handling of extended/special headers
in read-mode (adding new extended headers should be
less painful now).
- improved nts() function.
- removed TarFile.chunks datastructure which is not
(and was never) needed.
- fixed TarInfo.tobuf(), fields could overflow with too
large values, values are now clipped.