Support multiple exec statements

[deric]

Current implementation does not support complete definition of exec plugin (from wiki):

<Plugin exec>
  Exec "myuser:mygroup" "myprog"
  Exec "otheruser" "/path/to/another/binary" "arg0" "arg1"
  NotificationExec "user" "/usr/lib/collectd/exec/handle_notification"
</Plugin>

Only one Exec statement could be defined.

Moreover there's a missing space between arguments (see line 6)

<% @exec.each do |exec| -%>"<%= exec %>"<% end -%>

[blkperl]

This was merged in.