carbon installs itself to /opt/graphite instead of the current virtualenv

mkdir /tmp/fooenv; cd /tmp/fooenv; virtualenv .; bin/pip install carbon

In 0.9.10, that writes to /opt/graphite/bin/carbon-client.py instead of /tmp/fooenv/bin/carbon-client.py. This is more than a little annoying since it may clobber the user's last version of carbon-client.

A workaround is this:
bin/pip install carbon --install-option=--prefix=/tmp/fooenv

I suspect the fix is for https://github.com/graphite-project/carbon/blob/master/setup.cfg to not specify a prefix.