Manage error occuring with non-seekable stream such as URLConnection.
Force the use of the package's class loader since JMagick class may not be available with current Thread's class loader (eg. application servers such as JBoss AS 7...)
* Correct test of 4th byte of header
* Handle Photoshop 3's JPEG format
Merge pull request #19 from guinotphil/spifix

Fix issue with JMagick Spi Providers