bashrc: PS1: add git_ps1 from Ubuntu's /etc/bash_completion.d/git

Signed-off-by: Emilio G. Cota <cota@braap.org>
bashrc: PS1: enable flags for dirty + stashed changes

Signed-off-by: Emilio G. Cota <cota@braap.org>
Merge branch 'master' into flamenco

Signed-off-by: Emilio G. Cota <cota@braap.org>