vchoi_fork

[svn-r12784] 
Fixes for bugs 676, 228

676: both h5repack and h5diff use H5Dread. In the case of a "big"
dataset, use read/write by hyperslabs the same way h5dump uses. An
arbitrary value of 1GB was defined for "big", i.e, if the dataset is
greater than 1GB, then read/write by hyperslabs

228: use the file type in read/write by default. A new switch -n was
introduced if the user wants to use a native type, which was the
previous use by default.

Added a new test for h5repack that repacks a 1GB dataset

Tested: heping (serial, parallel), sol, copper