The JPEG plug-in has some recently identified problems in the XML
definition of JPEG metadata.

The metadata definition assumes that the JPEG image stream is a JFIF stream.
This is common but not universal, and is in fact mutually exclusive
to the most common format used in modern digital cameras (EXIF).

In particular both EXIF and JFIF specify that the SOI is immediately
followed by the marker appropriate for that interchange format
(app0JFIF or app1EXIF).
The present metadata is defined in a way which precludes the latter.

We need to fix the metadata specification to support both JFIF and
EXIF before FCS else it will be irreparably flawed and difficult to retrofit.

The required changes would not affect the structure of the metadata definition
so should be easy to do without consequences.

The changes required do not affect "API" In the traditional,
accepted sense of classes and methods but involve a revision of the
XML schema describing the metadata for the JPEG plug-in, and its
accompanying javadoc user documentation, but it does
affects behaviour visible to applications, considered to be part
of the specification, therefore a CCC request needs to be filed.

We also need to update implementation code which handles metadata to
properly return the updated metadata spec if requested by a client.