Bug 1259551 - Upgrade vendored virtualenv to 15.0.1; r=ted

While we're addressing virtualenv foo, let's ensure we are running
the latest version. This also pulls in newer versions of pip (8.1.1),
setuptools (20.3), and wheel (0.29.0).

MozReview-Commit-ID: G5uSy66Kd6u

python/virtualenv/virtualenv_embedded/activate.sh

@@ -2,7 +2,7 @@
 # you cannot run it directly
 
 deactivate () {
-    unset -f pydoc
+    unset -f pydoc >/dev/null 2>&1
 
     # reset old environment variables
     # ! [ -z ${VAR+_} ] returns true if VAR is declared at all