vchoi_fork

[svn-r19848] Bug 1917: big test failed especially in Widows.

big.c:
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.

H5FDstdio.c:
Removed an incorrect condition that whether STDIO VFD supports
larger than 32bits I/O depends on the support of fseeko.  Windows does not
use that. Instead, it uses _fseeki64 to support larger than 32bits I/O.

Tested: h5committest, jam (serial).