hdf5_der

[svn-r23886] Mutliple things happened in this commit.

1. Merged yesterday with hdf5_ff branch.
2. Fixed a couple of memory corruption, error handling issues.
3. Stable version of requests going through compactor, with new queue maninpulation routines
4. Tested and fixed bugs in compaction process. 
   Now compaction happens succesfully for mutliple dataspaces of the same 
   dataset. Memory descriptor gets constructed accordingly.
TODO:
  -- Have to call the write operations with merged requests from the request
  list.