Fix OSX failures (#85)

Fix "cd" overridden by RVM.
Don't try to uninstall virtualenv if pip is not installed.

common_utils.sh

@@ -18,6 +18,11 @@ if [ $(uname) == "Darwin" ]; then IS_OSX=1; fi
 # https://github.com/direnv/direnv/issues/210
 shell_session_update() { :; }
 
+# Workaround for https://github.com/travis-ci/travis-ci/issues/8703
+# suggested by Thomas K at
+# https://github.com/travis-ci/travis-ci/issues/8703#issuecomment-347881274
+unset -f cd
+
 function start_spinner {
     if [ -n "$MB_SPINNER_PID" ]; then
         return

osx_utils.sh

@@ -252,7 +252,8 @@ function make_workon_venv {
 
 function remove_travis_ve_pip {
     # Remove travis installs of virtualenv and pip
-    if [ "$(sudo which virtualenv)" == /usr/local/bin/virtualenv ]; then
+    # FIXME: What if virtualenv is installed but pip is not?
+    if [ "$(sudo which virtualenv)" == /usr/local/bin/virtualenv ] && [ "$(sudo which pip)" == /usr/local/bin/pip ]; then
         sudo pip uninstall -y virtualenv;
     fi
     if [ "$(sudo which pip)" == /usr/local/bin/pip ]; then