Possible fix for occasional failures on castoroides etc

It's annoying that the buildfarm animals running on older versions of
Solaris randomly fail with "Connection refused" errors, such as in
today's example:
http://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=castoroides&dt=2012-09-15%2015%3A42%3A52

I believe what's probably happening there is that the kernel has a small
hard-wired limit on the length of the postmaster's accept queue, and you
get this failure if too many connection attempts arrive faster than the
postmaster can service them.  If that theory is correct, we could
probably prevent these failures by reducing the number of tests run in
parallel, which could be done by adding sayMAX_CONNECTIONS=5
to the environment in which the regression tests run.  I'm not sure
though if that's "build_env" or some other setting for the buildfarm
script --- Andrew?
        regards, tom lane