image mime type detection failed.

Rev. 2.11 - 2013-02-24
* Fixed: image mimetype detection failed if EXIF was not installed on
the PHP server.
Rev. 2.12 - 2013-03-10
* Fixed: Decoding of html entities if added to the book metadata.
Requires added file EPub.HtmlEntities.php
Updated Zip.php to 1.38. Adding new parameter to addFile to force Store.

New files for the EPub rev. 2.50 beta code, adding EPub.NCX.php,
EPUB.OPF.php and Logger.php
EPub.250.php is a beta version of the new class,  splitting out the ncx
and opf to better handle these xml files. Levelling of chapters and
fiels added is supported in these as well, but still pending for the
EPub.250.php itself. I still have to figure out how the h*** I'm going
to do that while retaining backwards compatability.