BLD: Add "--exists-action w" to pip invocations

etc/ordered_pip.sh

@@ -5,7 +5,7 @@ while read line
 do     
     if [[ -n "$line" && "$line" != \#* ]] ; then
         # forward to pip any args after the reqs filename
-        pip install $line "${@:2}"
+        pip install --exists-action w $line "${@:2}"
         ((a = a + 1))
     fi
 done < $1

vagrant_init.sh

@@ -46,5 +46,5 @@ echo "Installing python package dependencies..."
 echo "Installing scipy..."
 pip install scipy==0.12.0 2>&1 >> "$VAGRANT_LOG"
 echo "Installing zipline dev python dependencies..."
-pip install -r /vagrant/etc/requirements_dev.txt 2>&1 >> "$VAGRANT_LOG"
+pip install --exists-action w -r /vagrant/etc/requirements_dev.txt 2>&1 >> "$VAGRANT_LOG"
 echo "Finished!"