vchoi_fork

[svn-r12610] Description:
    Add support for checksumming fractal heaps.  This is always enabled for
the heap header and indirect blocks (as they are "pure" metadata) and is
optional for direct blocks, since they may be used for "raw" data.

    Also, rearrange direct block routines in H5HFcache.c to be in a more
sensible location in the file.  (probably should have been a separate checkin,
since the diffs are mostly useless for this checkin... *sigh*)

Tested on:
    Linux/32 2.6 (chicago)
    Linux/64 2.6 (chicago2)