review start fo ssh-agent

Proposed start of ssh-agent for local passphrases in .bashrc:
```
env=~/.ssh/agent.env

agent_load_env () { test -f "$env" && . "$env" >| /dev/null ; }

agent_start () {
    (umask 077; ssh-agent >| "$env")
    . "$env" >| /dev/null ; }
```

- study meaning of agent.env
- review initialization of the ssh-agent, at least we should check that it is already running