Fix --eval output when using FISH

This commit fixes two problems with the output of `keychain --eval` when using FISH.

Firstly, you could not run `eval (keychain --eval)` because of missing semi-colons at the end of each line, which necessitated workarounds like `for e in (keychain --eval); eval "$e"; end`. You can see why with `echo (keychain --eval)`: all lines are joined, so directly evaluating it would execute commands like `set -x -U SSH_AUTH_SOCK /tmp/ssh-QdKWiXUO1468/agent.1468 set -e SSH_AGENT_PID`. Needless to say, programs were not able to connect to ssh-agent.  This is fixed by adding an appropriate `;` in the sed command.

Secondly, the use of `and` meant that, should an environment variable not exist already, evaluating the `--eval` output would not set it. This is fixed by removing the `and` from the sed command.

Note that I am using fish-2.0.0. I haven't tested with older versions, but I can't imagine why any problems would arise from these changes.