Fix assemblies not being resolved when a MSBuild project defines a reference search path via a PropertyGroup/ReferencePath which defines the path using $(SolutionDir).

src/Main/Base/Project/Src/Project/Solution/Solution.cs

@@ -317,6 +317,7 @@ namespace ICSharpCode.SharpDevelop.Project
 			changeWatcher.Disable();
 			changeWatcher.Rename(fileName);
 			this.fileName = fileName;
+			UpdateMSBuildProperties();
 			string outputDirectory = Path.GetDirectoryName(fileName);
 			if (!System.IO.Directory.Exists(outputDirectory)) {
 				System.IO.Directory.CreateDirectory(outputDirectory);
@@ -1178,6 +1179,7 @@ namespace ICSharpCode.SharpDevelop.Project
 			
 			string extension = Path.GetExtension(fileName).ToUpperInvariant();
 			newSolution.fileName = fileName;
+			newSolution.UpdateMSBuildProperties();
 			newSolution.isLoading = true;
 			try {
 				if (!SetupSolution(newSolution)) {
@@ -1190,6 +1192,12 @@ namespace ICSharpCode.SharpDevelop.Project
 			solutionBeingLoaded = null;
 			return newSolution;
 		}
+		
+		void UpdateMSBuildProperties()
+		{
+			MSBuildProjectCollection.SetGlobalProperty("SolutionDir", Directory);
+		}
+		
 		#endregion
 		
 		#region System.IDisposable interface implementation