hdf5_msb

[svn-r23237] Purpose: Implement H5Dscatter and H5Dgather

Description:
Adds 2 new API functions, H5Dscatter and H5Dgather.  H5Dscatter retrieves data
from a specified callback function and scatters it into a selection, defined by
a supplied dataspace, within a supplied memory buffer.  H5Dgather gathers data
from a selection within a supplied memory buffer and passes it in a contiguous
form to a supplied callback function.  Added tests for these functions

Tested: jam, ostrich, koala (h5committest); ummon