[Reproducible-builds] python-support umask affects reproducibility of built packages

[Daniel Kahn Gillmor]

Control: user reproducible-builds at lists.alioth.debian.org
Control: usertags 588746 + umask
Control: affects 588746 xtalk

Fixing the python-support umask issue for .private files would make more
packages build reproducibly.

For example, consider the xtalk package, which builds reproducibly
*except* for the umask difference in
usr/​share/​python-​support/​xtalk.​private, which appears to be generated by
python-support:

 https://reproducible.debian.net/rb-pkg/unstable/amd64/xtalk.html

        --dkg