Update lib/carbon/writer.py
Update lib/carbon/writer.py

Creating the directory tree with the proper umask/permissions in the environment. The new value of the umask will come from the Twisted parameter --umask. The permissions will now match the whisper archives.
krux/carbon,piotr1212/carbon,mleinart/carbon,criteo-forks/carbon,benburry/carbon,deniszh/carbon,iain-buclaw-sociomantic/carbon,kharandziuk/carbon,piotr1212/carbon,xadjmerripen/carbon,pratX/carbon,cbowman0/carbon,iain-buclaw-sociomantic/carbon,benburry/carbon,mleinart/carbon,lyft/carbon,JeanFred/carbon,johnseekins/carbon,lyft/carbon,deniszh/carbon,graphite-project/carbon,obfuscurity/carbon,johnseekins/carbon,xadjmerripen/carbon,criteo-forks/carbon,obfuscurity/carbon,krux/carbon,graphite-server/carbon,cbowman0/carbon,pu239ppy/carbon,pu239ppy/carbon,graphite-project/carbon,graphite-server/carbon,kharandziuk/carbon,JeanFred/carbon,pratX/carbon