hdf5_der

[svn-r20555] Purpose: Improve performance when edge chunk filters are disabled with no chunk
cache.

Description:
When edge chunk filters and the chunk cache are disabled, the library would
previously go through the lock/unlock routines then immediately evict the chunk
as is done for filtered datasets, even for the unfiltered edge chunks.  This
forced the entire chunk to be read/written, even if only part of the chunk was
selected.  Modified the chunk cache to detect this case, and read/write only the
selected portion directly from/to the unfiltered chunk.

Tested: jam, amani (h5committest, heiwa down), fedora