vpopmail - virtual domains for qmail

Here's a patch, from the FreeBSD port of 5.4.17, to
avoid a race condition in scanning a domain directory
for .qmail-style aliases. In the current code, there is
a time of check vs. time of use race condition: the
valias_select_names() routine does an opendir / readdir
/ closedir loop, counts the files, allocates memory,
and then does another opendir / readdir / closedir
loop. If anybody should create a new alias in the
(admittedly small) interval between the two loops, bad
things might happen. This patch does everything in a
single loop, dynamically realloc(3)'ing the aliases
buffer as necessary.

If the patch does not come through for any reason, it
is also available at
http://people.freebsd.org/~roam/patches/vpopmail/vpalias-dynalloc-names.pat
ch