hdf5_der

[svn-r20196] This checkin consists of the following:
A) - Changes to add the new tool "h5watch" to High Level
   - Changes to add three new High Level public routines for retrieving elements appended to a dataset

B) A patch from Mike M. to fix the H5Dflush/refresh problem:
src/H5Dpkg.h
src/H5Dint.c
src/H5D.c

C) Fix for an assertion failure in H5FS_sect_link_size() in H5FSsection.c
src/H5Dbtree2.c

h5committested; tested also on linew, duty, fred.