Fix for WPMU where IPN was failing.

git-svn-id: https://plugins.svn.wordpress.org/ebook-store/trunk@962260 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix for WPMU where IPN was failing, and readme.

git-svn-id: https://plugins.svn.wordpress.org/ebook-store/trunk@962261 b8457f37-d9ea-0310-8a92-e5e31aec5664