Patch #1484695 applied with rev 45954 introduced an
error in the creation of string header fields. The
stn() function used to zero-pad strings assumes that a
string to be put in an N character field, can be at
most N-1 chars long plus a '\0' char. This is wrong. An
N char field can store a N char string, the '\0' is
left out in this case.
The worst effect of this bug is that filenames that are
exactly 100 chars long will be silently truncated to 99
chars. Python 2.5 and 2.6 are affected.

Attached patch fixes the stn() function and adds a
testcase to test_tarfile.py.

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Applied in rev. 52431, 52432 (2.5).