hdf5

[svn-r19817] Bug 1917: Big.c test.

Changed the test to run Huge Dataset (tens of GB), Xtra large dataset(4GB big),
Large dataset (2GB big), or merely 1GB big, depending on if the file system
supports sparse file or if it supports larger than 32bigs I/O.

Tested: h5committest, jam (serial), Windows (Bangan which is Windows 7, 32bits).