Bug 741174 - Silent install option for maintenance service. r=bbondy

toolkit/mozapps/installer/windows/nsis/common.nsh

@@ -4861,6 +4861,11 @@
               StrCpy $AddStartMenuSC "1"
             ${EndIf}
 
+            ReadINIStr $R8 $R7 "Install" "MaintenanceService"
+            ${If} $R8 == "false"
+              StrCpy $InstallMaintenanceService "0"
+            ${EndIf}
+
             !ifndef NO_STARTMENU_DIR
               ReadINIStr $R8 $R7 "Install" "StartMenuDirectoryName"
               ${If} $R8 != ""