ext2fs updates from ffs

[Matthew Dillon]

:Hi again;
:
:Here is an updated patch.

    Thanks Pedro.  I will apply the brelse fixes, the i_next_alloc_block
    fix, and a few others to DragonFly.  We will have to forego the
    application of the ASYNC enhancements and most of the syntax changes
    (though I'll definitely keep the 'error =' syntax adjustments),
    mainly because we are too close to the release to test them and I
    don't want to create any accidental bugs.  ext2fs support is really
    just there for accessibility, we don't expect people to use ext2fs for
    a main filesystem in DragonFly.

					-Matt