Merge pull request #49 from marcusoftnet/FixingIgnoredTests

Fixing some failed and ignored tests
Make PathExtensions tests use mock file system

So that they do not depend on the presence of physical files and
directories (which are unlikely to exist on the build server)
Set up infrastructure for using MockFileSystem in tests
Using mockfilesystem from base in PathExtensionsTests
Rename FileSystem to RealFileSystem
Make FolderDirectoryTreeNodeTests use MockFileSystem
Make HtmlContentFormatterTests use MockFileSystem
Getting rid of System.IO usage as much as possible
Getting rid of System.IO in WhenMovingImages
Merge remote-tracking branch 'upstream/master'