Make Signup Drupal messages more user-generic

Issue Summary

The confirmation email text and reminder email text that display through drupal_set_message() are worded as though the person seeing the message is the one who has signed up (and usually they are), but if another module allows an admin to sign users up, the admin sees messages directed to "You" the signee. With a wording change, this becomes a non-issue:

"You will receive a confirmation email shortly which contains further information about this %node_type."
can be
"A confirmation email will be sent shortly containing further information about this %node_type."

And

"You will receive a reminder email !number !days before the %node_type."
can be
"A reminder email will be sent !number !days before the %node_type."

Patch to follow.