Incompatible changes in the Libraries API and SPI

Hi,
I am going to do several incompatible changes involving both libraries
API and SPI package.

The changes are:
1.) ContentType class is replaced by the String, this affects nearly all
the classes in the Libraries API and SPI.
2.) Removed getDescriptor method from LibraryType, Volume and 
VolumeProvider.  The descriptor is replaced by Look.
3.) Removed selectResource method from the Volume class, replaced by the
TemplateWizard.Iterator in the Lookup of the volume's Look.
4.) Change in the library-declaration.dtd
    <!ELEMENT volume (type, resource+) >
changed to
   <!ELEMENT volume (type, resource*) >
to allow empty volumes.

Tomas