Fix bad results on VS prebuild run

Design time build runs through very limited targets and does not provide
any libraries so we can skip weaving. VS runs normal build at some point
anyway so it should not hurt somebody but improve VS responsiveness
and user experience.

Author: alex-kulakov

MSBuild/DataObjects.Net.targets

@@ -21,7 +21,7 @@
         Inputs="@(IntermediateAssembly -> '%(FullPath)')"
         Outputs="@(IntermediateAssembly -> '%(FullPath).weaver-stamp')"
         DependsOnTargets="ResolveAssemblyReferences;_CopyFilesMarkedCopyLocal;$(XtensiveOrmBuildDependsOn)"
-        Condition="'$(XtensiveOrmSkipProcessing)'!='true'">
+        Condition="'$(XtensiveOrmSkipProcessing)'!='true' AND '$(DesignTimeBuild)' != 'true'">
   <Error Condition="!Exists('$(XtensiveOrmWeaver)')"
          Text="Weaver is not found at '$(XtensiveOrmWeaver)'" />
   <Message Importance="low" Text="Using weaver at '$(XtensiveOrmWeaver)'" />