buildfarm client release 4.18

I have just released buildfarm client version 4.18.

In addition to some minor fixes, there are two significant changes:

* The client now makes a determined effort to clean up any left over
build artefacts from previous runs at the start of a run. It also
tries to clean away old socket files. That means that manual fixes
are much less likely to be required, if the script has crashed or
the machine has crashed or restarted.
* There is a new config parameter "wait_timeout", which defaults to
undefined. If it is set then any run that takes longer than the
specified number of seconds is aborted. That means that runs that
get stuck will time out, and the whole animal won't be stuck and
requiring manual intervention. My test animal has a setting of 3 *
3600, i.e. 3 hours. There is some possible danger in this, that we
might miss bugs that cause us to get stuck, so at least some animals
should not use this feature.

The release can be downloaded from:
<http://www.pgbuildfarm.org/downloads/releases/build-farm-4_18.tgz>

cheers

andrew