add support for handle attribute in Format.WFST

[bartvde]

This is both available in WFS 1.0 and WFS 1.1.

From the schema:

<xsd:attribute name="handle" type="xsd:string" use="optional"><xsd:annotation><xsd:documentation>
               The handle attribute allows a client application
               to assign a client-generated request identifier
               to a WFS request.  The handle is included to
               facilitate error reporting.  A WFS may report the
               handle in an exception report to identify the
               offending request or action.  If the handle is not
               present, then the WFS may employ other means to
               localize the error (e.g. line numbers).
            </xsd:documentation></xsd:annotation></xsd:attribute>

[bartvde]

So the handle attribute can be present at different levels, i.e. e.g. both on the GetFeature as the Query level for read operations.

[bartvde]

All tests pass in FF5, TIA for any review.

[ahocevar]

All tests pass in Safari5 as well, and the patch looks good. Please commit.

[bartvde]

(In [12170]) add support for handle attribute in Format.WFST, r=ahocevar (closes #3412)