Automatically activate virtualenv when cd into project directory

auto_activate_virtualenv.sh

# Automatically activate virtualenv when using 'cd' (rewrite builtin cd function)
# Assuming current working directory is in a sub-directory of virtualenv directory
function cd {
    builtin cd "$@"
    # Check upper 4 directories
    if [-d "../bin" -a -d "../lib" -a -d "../include" -a -e "../.Python" \
        -a -e "../pip-selfcheck.json" ] ; then
        source ../bin/activate
    elif [  -d "../../bin" -a -d "../../lib" -a -d "../../include" -a -e \
        "../../.Python" -a -e "../../pip-selfcheck.json" ] ; then
        source ../../bin/activate
    elif [  -d "../../../bin" -a -d "../../../lib" -a -d "../../../include" \
        -a -e "../../../.Python" -a -e "../../../pip-selfcheck.json" ] ; then
        source ../../../bin/activate
    elif [ -d "../../../../bin" -a -d "../../../../lib" -a -d \
        "../../../../include" -a -e "../../../../.Python" -a -e \
        "../../../../pip-selfcheck.json" ] ; then
        source ../../../../bin/activate
    fi
}