Add separate obj directory for CF build to avoid corruption.

src/ProtocolBuffers/ProtocolBuffersCF.csproj

@@ -18,6 +18,7 @@
     <NativePlatformName>Windows Mobile 6 Professional SDK</NativePlatformName>
     <FormFactorID>
     </FormFactorID>
+    <BaseIntermediateOutputPath>objCF</BaseIntermediateOutputPath>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>