bash: Fix PROMPT_COMMAND for Gnome 3.7

gnome-terminal-3.7 changed behavior. When creating a new window or tab, it no
longer opens the new terminal in the same directory. Instead, it opens the new
terminal in $HOME.

To restore old behavior, the shell must request gnome-terminal to change
directories with a terminal escape sequence (that is `printf \033]$stuff`).
Luckily, /etc/profile.d/vte.sh:__vte_prompt_command() defines PROMPT_COMMAND to
print the needed escape sequence to restore the gnome-terminal's old behavior.