Build projects in correct order and allow for parallel builds.

Build projects in correct order and allow for parallel builds.

In tools/xbuild:
	* SolutionParser.cs (ProjectInfo.Dependencies): Change to a dictionary
	to keep track of corresponding ProjectInfo objects.
	(ParseSolution): Refactor to populate the ProjectInfo.Dependencies
	dictionary. Use AddBuildLevels to emit build levels to allow
	parallel builds.
	(AddProjectTargets): Dependency's projectInfo is directly available now.
	(AddBuildLevels): New. Emit items named BuildLevelN, where each level
	has projects that can be built in parallel. Lower levels represent
	dependencies for higher levels.
	(AddSolutionTargets): Instead of using CallTarget, directly use MSBuild
	task with the new BuildLevelN stuff. Also tell the user about disabled
	projects or missing project configs.
	(TopologicalSort): New.
	(Insert): New. Based on code from monodevelop.

In tools/xbuild/tests:

	* standalone/Project01: Update .sln.proj file.

svn path=/trunk/mcs/; revision=139933