Uncle Google speaks about this extension too

Change-Id: Ib757ea180fe570277d0cbe8a5ff4d6e30cce7cdb

filter/source/config/fragments/types/writer_MacWritePro.xcu

@@ -18,7 +18,7 @@
     <node oor:name="writer_MacWritePro" oor:op="replace" >
         <prop oor:name="DetectService"><value>com.sun.star.comp.Writer.MWAWImportFilter</value></prop>
         <prop oor:name="URLPattern"/>
-        <prop oor:name="Extensions"><value>mw</value></prop>
+        <prop oor:name="Extensions"><value>mw mcw</value></prop>
         <prop oor:name="MediaType"><value>application/macwriteii</value></prop>
         <prop oor:name="Preferred"><value>true</value></prop>
         <prop oor:name="PreferredFilter"><value>MacWritePro</value></prop>