$upload should look something like:
Array (
[file] => /home/dac514/public_html/bdolor/wp-content/uploads/sites/2/2013/04/Hello-World-13662149822.epub
[url] => http://localhost/~dac514/bdolor/helloworld/wp-content/uploads/sites/2/2013/04/Hello-World-13662149822.epub
[type] => application/epub+zip
)
'pressbooks_current_import' should look something like:
Array (
[file] => '/home/dac514/public_html/bdolor/wp-content/uploads/sites/2/imports/Hello-World-1366214982.epub'
[file_type] => 'application/epub+zip'
[type_of] => 'epub'
[chapters] => Array (
[some-id] => 'Some title'
[front-cover] => 'Front Cover'
[chapter-001] => 'Some other title'
)
)