Duplicate peers

Because peerGetSomeParent and then peerGetAllParents are both called
in the NEVER_DIRECT case (e.g., accelerators), the list of peers to
use will contain a duplicate; whatever peerGetSomeParent returns will
be in the list twice, and if it's the first peer (lexically in the
conf file), it'll be twice in a row. This isn't good, especially for
round-robin accelerator setups.
Attached patch skips duplicates of the first peer list entry (in the
long term, this might need to be reworked, but this seems like a low-
cost way to improve things for the time being).
<http://www.squid-cache.org/bugs/show_bug.cgi?id=2378>

--
Mark Nottingham       mnot_at_yahoo-inc.com