fixup??? vcxproj: adjust for the reftable changes

Needed by Git for Windows' recent vcxproj adjustments ("vcxproj: unclash
project directories with build outputs").

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

contrib/buildsystems/Generators/Vcxproj.pm

@@ -245,7 +245,7 @@ EOM
 EOM
       if (!($name =~ /xdiff|libreftable/)) {
         print F << "EOM";
-    <ProjectReference Include="$cdup\\reftable\\libreftable\\libreftable.vcxproj">
+    <ProjectReference Include="$cdup\\reftable\\libreftable.proj\\libreftable.vcxproj">
       <Project>$uuid_libreftable</Project>
       <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
     </ProjectReference>