vchoi_fork

[svn-r12607] Description:
    Tweak the library's new faster fletcher32 algorithm to always produce the
same checksum as the previous fletcher32 code in the fletcher32 I/O pipeline
filter and switch the filter to use the library's version of the algorithm.

Tested on:
    Linux/32 2.6 (chicago)
    Linux/64 2.6 (chicago2)
    Too minor to require h5committest