Previously solr depended on a package autoload to load in the pxml
package.  Now explicitly require the more modern pxml-sax package.

Tests added for:       no
make test-suite run?   yes
Documentation changes? no

<release-note>
rfe16091: use new :pxml-sax in solr and aws repos

The direct client library agraph.fasl will now use the pxml-sax
package rather than the pxml package.  Existing Lisp code that
uses agraph.fasl and also pxml should be changed to use pxml-sax.

</release-note>

Change-Id: I953a716eddfc53fd30478a27812ad5caf7a3ec35
Reviewed-on: https://gerrit.franz.com:9080/13057
Reviewed-by: John Foderaro <jkf@franz.com>
Reviewed-by: Mikel Bancroft <mikel@franz.com>
Reviewed-by: Ahmon Dancy <dancy@franz.com>
Tested-by: Ahmon Dancy <dancy@franz.com>