Fixes the profiles-plugin

An error was introduced with 7f75bb9, which uses special vars. This is the
fix.
Merge pull request #3299 from apoxa/fix-profiles

Fix for the profile plugin.
Force ssh-agent output to use bourne-style syntax

On systems where the shell cannot be changed because of a strict
security policy, ssh-agent will use the syntax of whatever the
default $SHELL is.
For instance, if the default shell is tcsh, ssh-agent will use the
c-shell style (setenv).

This change forces ssh-agent to use bourne-style syntax since that
has to be later interpreted by zsh. Consequently, the environment
file will contain `export' statements from now on (instead of
`setenv').