[docs] doc bug: undocumented fields in tarfile.TarInfo

[Ravi Pinjala]

Hi,

In the tarfile.TarInfo class, the devmajor and devminor fields are 
undocumented. tarfile supports character and block devices, but the 
undocumented fields are the only way to access the major/minor device 
numbers and actually make use of this support. These fields are only set 
for character and block devices.

--Ravi Pinjala