PHP exec() uses sh -c which is dash on Ubuntu. Dash echo does not
support -en flag, breaking the echo CmdStager flavor. Switch to
printf (octal) and bourne (base64) flavors which work in dash.
Also split backup_and_poison into backup_config and poison_dot so
CmdStager chunks don't overwrite the backup table, and escape
backslashes in SQL to preserve octal/hex sequences through MySQL.
Valentin Lobstein
4aeacb7456