Allow sourcing envsetup from anywhere

    # e.g.

    # ENVSETUP_NO_COMPLETION=adb # -> disable adb completion

    # ENVSETUP_NO_COMPLETION=adb:bit # -> disable adb and bit completion

    local T=$(gettop)

    for f in ${completion_files[*]}; do

        f="$T/$f"

        if [ ! -f "$f" ]; then

          echo "Warning: completion file $f not found"

        elif should_add_completion "$f"; then