Consistently silence pushd and popd in hooks

Consistently redirect the output of pushd and popd to /dev/null in
cartridge scripts.
Make a few clarifications in the README for PHP
Merge pull request #1122 from smarterclayton/improve_php_cartridge_readme

Merged by openshift-bot
Merge pull request #1110 from Miciah/silence-pushd-and-popd

Merged by openshift-bot