Upgrade virtualenv, fix issue 181

This commit fixes #181 by upgrading `virtualenv` to the 1.9 release series.

I also removed references to internal twitter servers that don't resolve publicly.


There's a bug in `virtualenv` 1.7, as documented here: https://bugs.launchpad.net/ubuntu/+source/python2.7/+bug/1115466

The Ubuntu thread offers a workaround, but upgrading `virtualenv` fixes the problem.

This commit passes all `pants` tests on my development VM:

    =========================================================================== 76 passed in 0.72 seconds ============================================================================
    tests.python.twitter.pants.base.base                                            .....   SUCCESS
    tests.python.twitter.pants.buildtimestats.buildtimestats                        .....   SUCCESS
    tests.python.twitter.pants.cache.cache                                          .....   SUCCESS
    tests.python.twitter.pants.commands.commands                                    .....   SUCCESS
    tests.python.twitter.pants.fs.fs                                                .....   SUCCESS
    tests.python.twitter.pants.java.java                                            .....   SUCCESS
    tests.python.twitter.pants.python.test_antlr_builder                            .....   SUCCESS
    tests.python.twitter.pants.python.test_python_chroot                            .....   SUCCESS
    tests.python.twitter.pants.python.test_subprocess_call_with_args                .....   SUCCESS
    tests.python.twitter.pants.python.test_thrift_namespace_packages                .....   SUCCESS
    tests.python.twitter.pants.reporting.reporting                                  .....   SUCCESS
    tests.python.twitter.pants.scm.scm                                              .....   SUCCESS
    tests.python.twitter.pants.targets.targets                                      .....   SUCCESS
    tests.python.twitter.pants.tasks.tasks                                          .....   SUCCESS
    tests.python.twitter.pants.utils                                                .....   SUCCESS