PS1 is not supposed to be an environment variable (i.e. will not
be listed in `printenv` but only in `set`). Its value should also
be shell-specific.
With this commit we can stop exporting a static PS1 as env var on
the java side.
The prompt would now indicate whether the current user is root.
The previous patched session.c just took the existing environment
and kept it. The new copies over a few specific variables needed
but otherwise does the normal setup.
Fixes#341 (TERM being ignored).
Fixes#290 (SSH_CONNECTION/SSH_CLIENT/SSH_TTY not setup).
Fixes https://github.com/termux/termux-app/issues/108 (SSH agent
forwarding not working).
Fredrik Fornwall
Leonid Plyushch
Tom Yan