contribution page should default to not sending a receipt

Currently, the is_email_receipt field in the civicrm_contribution_page table defaults to 1.

However, to effectively send a receipt, the user needs to enter the receipt_from_email value. When filling in the form, this field is required. However, it's possible to create a contribution page and never visit the tab on the form with this option. In this case, a receipt will be sent possibly without a from email address value. This result in an index not found error and many email relays will reject the message (and the messages received will appear strange and un-professional).

It seems better to default to not send a receipt. Then, if someone chooses that option, they can't save that option without filling in the required field.

If that's acceptable I can make the relatively small code change.

This is not urgent... it can get pushed to 4.2.