Add hacking MSBuild solution for MSBuild libraries.
implement various not-implemented types in Microsoft.Build.dll.
Add missing ProjectInstance family.
implement some MS.Build members as well as adding missing members.
MS.Build.dll: Add more missing members and implementation for some members.
Add missing tests in csproj.
Add IBuildEngine3 and IBuildEngine4.
Add IBuildEngine3 and IBuildEngine4 to csproj.
ToolLocationHelper is now used in MS.Build.dll too (as internal).
Add ToolLocationHelper and co. to MS.Build.dll (as internal).
implement ProjectCollection.Toolsets.
update MS.Build.csproj.
fix test csproj build.
Fix MS.Build.Tasks.csproj build too.
Add ToolsetTest and fix Toolset construction.
update MS.Build test csproj.
Add BuildEventContext.
add BuildEventContext to .csproj.
Fix net_4_0 build.
update MS.Build csproj to the latest status.