bisect-runner.pl needs to probe DB_File.xs before running Configure

bisect-runner.pl needs to probe DB_File.xs before running Configure

Commit f2f0a0ff7250e0ba (in Nov 2011), consolidated all the code that
patches extensions. As a side effect, it moved all extension patching
after Configure is run. Unfortunately this introduced a bug, because one
test of DB_File.xs was to change the arguments to Configure to skip building
DB_File at all if it's too old. Return this logic to before when Configure
is run, so that bisect-runner.pl can once again build 5.005 and earlier on
machines with the Berkley DB headers installed, by forcibly skipping the
build of DB_File there.