add a class constant for PUT requests
pull HttpException changes
add 2 new assertion methods
modify items/add to use PUT requests

Instead of requiring a POST of type multipart/form-data,
require a PUT of type application/x-ald-package. This is
more consistent to item descriptions / downloads and also
eliminates an old, unnecessary need to translate the data
to the old format.

Adjust the code accordingly: instead of the $_FILES array,
read the "php://input" stream in a temp file. Require the
Content-Length to be specified.
items/add: Move the temp file only after it is validated.
Delete the uploaded file if the DB insertion fails.
fix items/add: use normal file moving

The previously used move_uploaded_file() only
works for files uploaded with the regular POST
mechanism used before.
refactoring: for the package file name, just use the ID.
fix: temp file is automatically deleted when handle is closed
fix: correct boolean check
delete long obsolete schema file
Merge pull request #26 from maul-esel/rework-item-API

Rework item API