adding a way to open a directory

and a test for such.
basic directory iteration via plx::FilesInfo

incomplete, the buffer to read the directory info needs to be of
variable size.
increase the re-ord limit

Now to 30
files_info.h was not compiling

got checked in with a WIP piece.
another fix to files_info.h

same deal.
adding linked_buffers

no tests yet.
plx::files_info first cut

It iterates properly and quickly enough.

Also the missing test for linkedbufers