pgbuildfarm - client-code: add support for web proxy if farm member

Log Message:
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add support for web proxy if farm member needs one to get through a firewall
to report results - needed for prospective AIX member.

Modified Files:
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client-code:
build-farm.conf (r1.7 -> r1.8)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbuildfarm/client-code/build-farm.conf.diff?r1=1.7&r2=1.8)
run_web_txn.pl (r1.1 -> r1.2)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbuildfarm/client-code/run_web_txn.pl.diff?r1=1.1&r2=1.2)