Ignore failures when registering firewall exceptions

There appear to be bugs in the WiX firewall extension that causes errors on
install/upgrade in some scenarios (seemingly where existing fw exceptions for
Moonlight exist as in #1309).

Since a firewall exception really only provides minimal benefits for us in the
default configuration of Windows Firewall (outgoing: allow, incoming: deny) due
to WFP's stateful treatment of solicited unicast/multicast UDP traffic, let's
allow it to silently fail and not abort the whole installation.

wix/Moonlight/Product.wxs

@@ -101,6 +101,7 @@
               Source="$(var.BuildDir)\app\$(var.Configuration)\Moonlight.exe">
           <fire:FirewallException Id="MoonlightFirewallException"
                                   Scope="any"
+                                  IgnoreFailure="yes"
                                   Name="$(var.FullName)" />
         </File>
       </Component>