hdf5_ep

[svn-r1276] H5D.c:
H5F.c:
H5Flow.c:
H5Fprivate.h:
    Joined work by Quincey, Robb and me to eliminate the initial writes
    of BOOTBLOCK when the file is first created.  Also, eliminate the
    repeatedly encoding of BOOTBLOCK in the flushing code.  Introduced
    the eof_written flag to indicate when it is not necessary to go
    do a dumb write at eof.
    (But something is not right if the userblock is not zero.)

H5Fmpio.c:
    Added code to allow setting the MPIO debug output mask via
    the environment variable H5F_mpio_Debug.