hdf5_msb

[svn-r16380] Purpose: Enable copying of dense attributes

Description:
Attribute object copy routines have been moved from H5Oattr.c to H5Aint.c.
These routines are now shared between compact and densely stored attributes.
New routines written to support the copying of dense attributes.  This patch wasmostly written by Peter Cao.

Tested: jam, smirom (h5committest)