Add validation of XML-RPC request data

Validation of pifr.queue and basic validation pattern/framework.

Needs documentation, test, and other methods validated.

Also need to remove stuff like:

      pifr_debug(t('XML-RPC batch(): missing project data for branch: (b: @identifier; p: @project_identifier).',
                   array('@identifier' => $branch['client_identifier'], '@project_identifier' => $branch['client_identifier'])));

once proper validation is in place.

#1: 597644-xmlrpc-validation.patch queued for re-testing.

Previous patch contained debug code that caused test failure. Removed debug code, added documentation and a few additional error messages.

Test, and code cleanup.

Committed.