* A new option -dns is introduced that enables name lookups in
-connect and -addnode, which is not enabled by default,
as it may be considered a security issue.
* A Lookup function is added that supports retrieving one or
more addresses based on a host name
* CAddress constructors (optionally) support name lookups.
* The different places in the source code that did name lookups
are refactored to use NameLookup or CAddress instead (dns seeding,
irc server lookup, getexternalip, ...).
* Removed ToStringLog() from CAddress, and switched to ToString(),
since it was empty.
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