When parsing entries from /etc/hosts file, they are all lowered
(see bug 3040). If cache_peer hostname is uppercase, it will
lead to DNS resolution failure. Lowering cache_peer host fixes
this issue.
This change may expose broken Squid configurations that
incorrectly relied on non-lowercase peer host names to
bypass Squid's "is this cache_peer different from me?"
check. Though such configurations should encounter
forwarding loop errors later anyway.