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.

one-time write to the mode, then all works. However, if no such write
is done, the variable always remains zero. I have used the memory
debugger as well as shuffled the code around and used guard variables
nothing changed. The problem always moved with the changes I did. So
I now consider the one-time write a usable work-around, because it
definitely fixes the issue even though it does not explain why it
happens.

we needed to release ALL resources (including file handles!) only
after the the async writer thread has terminated (else it may access
them). In this case, we had a file handle leak, because the handle was
sometimes only opened in the async writer, but the close was attempted
before the writer even started (in some cases).

...after we seem to have identified the root cause of the segfault.
I leave them commented out so that we can re-activate it if need
arises (aka "get some practice drill first").