Concurrency issue handled in BuildSession.cs

I added some lock blocks in BuildSession.cs and that seems to solve the concurrency problem I experienced some days ago (see https://groups.google.com/forum/?fromgroups=#!topic/structuremap-users/Mm-dCtEr_nY). In InterceptorLibrary.cs I just deleted a duplicate check. Since I'm new to GitHub, please let me know if I did something the wrong way.
Thanks,
S.M.