hdf5_ep

[svn-r16214] Added HDlseek to the H5FD_core_truncate function in H5FDcore.c to rewind the file pointer
to the beginning of the file.  Otherwise, the file might be re-extended later on Open VMS.
Also updated the return value for the HDlseek to be more appropriate.

Tested 1.8 on Open VMS.