Bug 930808 - Upgrade virtualenv to 12.0.2; r=glandium

Source archive downloaded from
https://pypi.python.org/packages/source/v/virtualenv/virtualenv-12.0.2.tar.gz
and uncompressed into python/virtualenv. The egg-info directory was
removed.

python/virtualenv/virtualenv_embedded/activate_this.py

@@ -13,7 +13,7 @@ except NameError:
 import sys
 import os
 
-old_os_path = os.environ['PATH']
+old_os_path = os.environ.get('PATH', '')
 os.environ['PATH'] = os.path.dirname(os.path.abspath(__file__)) + os.pathsep + old_os_path
 base = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 if sys.platform == 'win32':