hdf5_msb

[svn-r19217] Bug 1986, error1.

It is an error to use the condition H5_HAVE_FSEEK64 to control the definition
of HDlseek. It caused errors in AIX where lseek64 is available.

Replaced it with H5_HAVE_LSEEK64. Also added the missing HDstrcasecmp macro.

Tested: AIX using default and --disable-largefile.