3.9 broke transients.  Prevents use of blockchain api when in preview mode.

git-svn-id: https://plugins.svn.wordpress.org/btc-exchange-widget/trunk@898394 b8457f37-d9ea-0310-8a92-e5e31aec5664
version

git-svn-id: https://plugins.svn.wordpress.org/btc-exchange-widget/trunk@898396 b8457f37-d9ea-0310-8a92-e5e31aec5664
doc update

git-svn-id: https://plugins.svn.wordpress.org/btc-exchange-widget/trunk@898397 b8457f37-d9ea-0310-8a92-e5e31aec5664