Add equality check to update_cron() interval calc

Problem/Motivation

If a release is outstanding and email interval is set to eg 1 day, and cron runs hourly, the email will be sent an hour later each day.

Steps to reproduce

Setup as above.

Proposed resolution

in update_cron() in update.module

 if (($request_time - $last_check) > $interval) {
if (($request_time - $last_email_notice) > $interval) {

replace '>' with '>='

Remaining tasks

add patch if agreed

User interface changes

none

Introduced terminology

none

API changes

Data model changes

Release notes snippet