Detect a lack of tables in HTML responses and raise an Exception.

git-svn-id: https://plugins.svn.wordpress.org/inline-google-spreadsheet-viewer/trunk@980462 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated FAQ, readme, version bump to 0.4.7.1.

git-svn-id: https://plugins.svn.wordpress.org/inline-google-spreadsheet-viewer/trunk@980464 b8457f37-d9ea-0310-8a92-e5e31aec5664