Initial commit of DNS code
Updated CMake files -- added libunbound linker flag

CMake config file written, but was unable to test/get it working
properly because of a bug in CMake with functions related to
find_package.  Simple "-lunbound" flag used in its stead for now.  May
not build on non-Linux systems, not sure yet.
ipv4 and ipv6 resolution working

IPv4 and IPv6 name resolution working.
Unit tests written (and passing).
net_node.{h,inl} code modified to use DNS seeds.
Use the loop iterator, previous version of me.
seed node DNS code updated to use DNSResolver

Also implemented rudimentary IPv6 support, but commented it out because
it's not widely supported by ISPs for now, and thus is not currently
supported by Monero.
Monero addres from DNS TXT record implemented, tests pass

Still need to deal with DNSSEC and optional fields in the TXT record.
Simplewallet should now resolve urls to addresses

Simplewallet should now do a DNS query on an address if it fails to
convert the given string to a binary representation of an address
(base58->binary).  It will prompt the user, telling of what the "url"
passed was, what monero address it translated to, and whether or not
DNSSEC validation was a success, and ask for a confirmation that these
are all acceptable.
change to allow (at least a bit) for multiple TXT records
Fixed CMake search for libunbound

As it turns out, some of CMake's built-in modules for detecting headers
and libraries don't work if you have certain compiler flags set, such as
-Werror=old-style-definition, as they do "int main()" rather than
"int main(void)".  Having CMake search for libs before compiler flags
are set alleviates this issue, and I believe the underlying issue will
be fixed in future releases of CMake.
Fixed artifacts from cherry-picking devel->master
Added function to check syntax of URL for DNS lookup

For now, simply checks for '.' character, but that will be easy to
change in the future if necessary/desired.