WL#3193: DD: Reclaming of free extents

If a table make all pages free within a extent.
The extent is still not returned to the tablespace (for usage by other tables)

This WL is about making this possible.
The code to do so is trivial, except when you get to the recovery part.
  The undo logging of these operation has to be thought about long and hard :-)

http://bugs.mysql.com/?id=17605 is a special case of this that relates to LCP's.