host_list: huge performance increase, esp for many hosts

Before I defecate on the implementation of rcpt_to.in_host_list, allow me to first point out the one area where it excels:

loaded 90822 hosts
loading config took 0.066 seconds (array)
loading config took 0.087 seconds (array+toLowerCase())
loading config took 0.152 seconds (object+toLowerCase())

That's right, the existing implementation is fastest as loading the config file to an array. But it's all downhill from there. In the next test, we look up a hostname in the list, 90,822 times (to average the lookup time):

searching config took 1662.722 seconds (array)
searching config took   87.560 seconds (array (lc during load))
searching config took    0.208 seconds (object (lc during load))
host_list: updated tests
Merge pull request #595 from msimerson/host_list

host_list: huge performance increase, esp for many hosts