Update VisualStudio.gitignore

The current pattern for NuGet doesn't work for sub-folders, also commented elsewhere here, and since by  default Visual Studio creates the packages folder one level below the root, the current exclude here doesn't work in those cases.
Fixed pattern for excluding nuget packages so that it works both for top level package folder and for any lower level package folders.  Re-include patterns fixed the same way.
I have written a blogpost here http://geekswithblogs.net/terje/archive/2014/07/03/gitignorendashhow-to-exclude-nuget-packages-at-any-level-and-make.aspx  with all the details, also what effect the different patterns have. 
I have also discussed this with the product group at MS, and got affirmative from them.