[Mono-list] xbuild uses 2.0.5.0 version of System.dll when no explicit version specified

[William S.]

I'm using mono 2.0.1 under OSX, installed from Novell's installer. It
seems that xbuild wants to use the "newest" version of assemblies
referenced in a .csproj file. In this case it picks up version 2.0.5.0
of the System.dll (used for silverlight?) which seems to have fewer
members than the version 2.0.0.0. Here are the files I used to test
and the output:

-- Foo.cs
using System.CodeDom.Compiler;

class Foo {
 GeneratedCodeAttribute a;
}
-- Foo.csproj
<Project DefaultTargets="Build"
xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
 <PropertyGroup>
   <OutputType>Library</OutputType>
   <AssemblyName>Foo</AssemblyName>
 </PropertyGroup>
 <ItemGroup>
   <Reference Include="System" />
 </ItemGroup>
 <ItemGroup>
   <Compile Include="Foo.cs" />
 </ItemGroup>
 <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
</Project>
-- xbuild output
XBuild Engine Version 0.1
Mono, Version 2.0.1.0
Copyright (C) Marek Sieradzki 2005. All rights reserved.

Build started 11/21/2008 6:59:42 PM.
__________________________________________________
Project "/private/tmp/Foo.csproj" (Build target(s)):

Target PrepareForBuild:
               Configuration:  Platform:

Target ResolveAssemblyReferences:

Target CoreCompile:
               Tool
/Library/Frameworks/Mono.framework/Versions/2.0.1/bin/gmcs execution
started with arguments: /noconfig /out:Foo.dll Foo.cs /target:library
/unsafe- /reference:/Library/Frameworks/Mono.framework/Versions/2.0.1/lib/mono/gac/System/2.0.5.0__7cec85d7bea7798e/System.dll
/warn:2
Foo.cs(1,14):   error CS0234:  The type or namespace name `CodeDom'
does not exist in the namespace `System'. Are you missing an assembly
reference?
Foo.cs(1,14):   error CS0234:  The type or namespace name `CodeDom'
does not exist in the namespace `System'. Are you missing an assembly
reference?

Build succeeded.
        0 Warning(s)
        3 Error(s)

Time Elapsed 00:00:00.3583950

I can force xbuild to use the proper version by explicitly asking for
version 2.0.0.0 in the .csproj file, but does anyone know of a better
way?