Use nicer labels for wxWidgets property sheets in MSVS UI

No real changes, just use the same _PropertySheetDisplayName element as
the standard style sheets use to show a slightly more user-friendly
label in the Property Sheet manager window in MSVS.

build/msw/wx_setup.props

@@ -1,5 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <_PropertySheetDisplayName>wxWidgets Setup Options</_PropertySheetDisplayName>
+  </PropertyGroup>
+
   <PropertyGroup Label="UserMacros">
     <wxVersionString>315</wxVersionString>
     <wxShortVersionString>31</wxShortVersionString>

wxwidgets.props

@@ -7,6 +7,10 @@
     tag to it.
   -->
 <Project ToolsVersion="4.0" InitialTargets="CheckWXLibs" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <_PropertySheetDisplayName>wxWidgets</_PropertySheetDisplayName>
+  </PropertyGroup>
+
   <ImportGroup Label="PropertySheets">
     <Import Project="build/msw/wx_setup.props" />
     <Import Project="build/msw/wx_local.props" Condition="exists('build/msw/wx_local.props')" />