hdf5_ep

[svn-r4017] Purpose:
    Code cleanup
Description:
    Several system header files needed to be included on Linux machines to
    get the prototypes for some of the system calls we are using.
Solution:
    Added a new feature test macro for including the <features.h>
    header on Linux machines, to set up compile macros for system header
    files.
Platforms tested:
    Linux (eirene), FreeBSD 4.3 (hawkwind)