filter: mark XLSX/PPTX filter as SUPPORTSSIGNING

Given that all DOCX signing code is in xmlsecurity and it wasn't
DOCX-specific, this works out of the box.

Change-Id: I18429f63c125a43346e9e52021e1b7e33b300af4

filter/source/config/fragments/filters/calc_MS_Excel_2007_XML.xcu

@@ -16,7 +16,7 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
 -->
 <node oor:name="Calc MS Excel 2007 XML" oor:op="replace">
-    <prop oor:name="Flags"><value>IMPORT EXPORT ALIEN 3RDPARTYFILTER PREFERRED ENCRYPTION PASSWORDTOMODIFY</value></prop>
+    <prop oor:name="Flags"><value>IMPORT EXPORT ALIEN 3RDPARTYFILTER PREFERRED ENCRYPTION PASSWORDTOMODIFY SUPPORTSSIGNING</value></prop>
     <prop oor:name="UIComponent"/>
     <prop oor:name="FilterService"><value>com.sun.star.comp.oox.xls.ExcelFilter</value></prop>
     <prop oor:name="UserData"/>

filter/source/config/fragments/filters/impress_MS_PowerPoint_2007_XML.xcu

@@ -16,7 +16,7 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
 -->
 <node oor:name="Impress MS PowerPoint 2007 XML" oor:op="replace">
-    <prop oor:name="Flags"><value>IMPORT EXPORT ALIEN 3RDPARTYFILTER PREFERRED ENCRYPTION PASSWORDTOMODIFY</value></prop>
+    <prop oor:name="Flags"><value>IMPORT EXPORT ALIEN 3RDPARTYFILTER PREFERRED ENCRYPTION PASSWORDTOMODIFY SUPPORTSSIGNING</value></prop>
     <prop oor:name="UIComponent"/>
     <prop oor:name="FilterService"><value>com.sun.star.comp.oox.ppt.PowerPointImport</value></prop>
     <prop oor:name="UserData"/>