pgbuildfarm - client-code: vpath logic bug fix vpath still needs a bit

Log Message:
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vpath logic bug fix
vpath still needs a bit more to learn which files to ignore - unfortunately
the postgres vpath process doesn't leave the source dirs completely
pristine.
But for now it seems to work, although it might do builds oftener than
necessary.

Modified Files:
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client-code:
run_build.pl (r1.27 -> r1.28)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgbuildfarm/client-code/run_build.pl.diff?r1=1.27&r2=1.28)