- DirectoryReader is extracted to separate header
- FileSystem.cxx/FileSystem.hxx/DirectoryReader.hxx moved to fs/ subdir
- Functions return true on success, instead of 0 (where applicable)
- ReadLink return result instead of out parameter
- UnlinkFile is renamed to RemoveFile
- CheckExists/CheckIsRegular/CheckIsDirectory are renamed
  to PathExists/FileExists/DirectoryExists

This file was used previously to force C++ linkage.
It's no longer required because most of the code is C++ anyway.

This reverts commit f56c6a18.  This
fix is not necessary anymore because clients are now being deleted by
the timer callback.

Don't use a global loop over the whole client list.

Fixes assertion failure (regression).