hdf5_chunking_query_bmr

[svn-r19248] Description:
	Bring r19247 from trunk to 1.8 branch:

    Bring r19246 from Coverity branch to trunk:

    Improve metadata "accumulator" for files to track the dirty region within
the accumulator data.  This allows the accumulator to drop clean data and
reduces the number of I/O operations when it is dirtied.

    This is progress toward Bz#1142 - speeding up the fheap test (which it
doesn't help much, actually, but it does help other aspects of file I/O).

Tested on:
    FreeBSD/32 6.3 (duty) in debug mode
    (h5committested on trunk)