Max size is now 32K.

This resulted in wrong values. The most prominent victim was the
directory creation mode, which was set to zero in some cases. For
details, see related blog post:
http://blog.gerhards.net/2009/10/another-note-on-hard-to-find-bugs.html

This replaces the improper bugfix from two commits ago with a proper one.

Most severely affected omfile. The problem was that some buffers were
freed before the asynchronous writer thread was shut down. So the
writer thread accessed invalid data, which may even already be
overwritten. Symptoms (with omfile) were segfaults, grabled data
and files with random names placed around the file system (most
prominently into the root directory). Special thanks to Aaron for
helping to track this down.

Problems could lead to abort and/or memory leak. The module is now hardened in a very
conservative way, which is sub-optimal from a performance point of view. This should
be improved if it has proven reliable in practice.