gitian: attempt to fix tarball determinisim

Needs 0.10 backport.

Rebuilding v0.10.0rc1 with these changes yields:
```
e4b60408c8917c3a1420529b6b4d9eff6fe080e4c7db86240effd0903f341dda  bitcoin-0.10.0-osx-unsigned.dmg
8cf94292cd7b936aa8f70cc3a550120842206e577cb22d448211093a57b95a48  bitcoin-0.10.0-osx-unsigned.tar.gz
26f5aa7914e2a25112b01bb5920d87e003e49c806c9a489ab80edbe7e1e47595  bitcoin-0.10.0-osx64.tar.gz
b074c4ba6c03b6045de61e521c6d47b2764a33a6c7d4f102dcdb72a9fec75601  src/bitcoin-0.10.0.tar.gz

504b6cb989b2f6967e3aa9ef1fd9ec15aaa28b060351f064323f3972cc199320  bitcoin-0.10.0-win32-setup.exe
24a94035641cbb84d9f8d04e290e1aa008346fc8b867029717475e2991d510a6  bitcoin-0.10.0-win32.zip
835559d963cb7d1e6fb594f15e19b4c46b811deb6b78afa25621f62af8be73ae  bitcoin-0.10.0-win64-setup.exe
d89d976778c8c1fd752e1171a4221bdfa26c626b342a9d5c21570c66903ea76f  bitcoin-0.10.0-win64.zip
b074c4ba6c03b6045de61e521c6d47b2764a33a6c7d4f102dcdb72a9fec75601  src/bitcoin-0.10.0.tar.gz

bad06e24032c6aafaeae21a44a1001de5d049191a86f61261e046c4b92796767  bitcoin-0.10.0-linux32.tar.gz
f1d016975a99910c7a7037fca0b3837446e56f17675f160597e10c5ef2c81a5d  bitcoin-0.10.0-linux64.tar.gz
b074c4ba6c03b6045de61e521c6d47b2764a33a6c7d4f102dcdb72a9fec75601  src/bitcoin-0.10.0.tar.gz
```
I'm testing locally with lxc, but it'd be nice to have someone else with lxc confirm they match.