[MCL-2627] Launcher will not download game over IPv6

The launcher won't work over IPv6. My network has DNS64+NAT64 at a router/ISP level, so there's no need for the remote host to support IPv6, but the client clearly does not:

Bootstrap (v5)
Current time is Jun 5, 2014 12:27:27 PM
System.getProperty('os.name') == 'Linux'
System.getProperty('os.version') == '3.14.5-1-ARCH'
System.getProperty('os.arch') == 'amd64'
System.getProperty('java.version') == '1.7.0_55'
System.getProperty('java.vendor') == 'Oracle Corporation'
System.getProperty('sun.arch.data.model') == '64'

Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 2/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 3/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 4/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 5/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 6/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 7/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 8/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 9/10)
Exception: java.net.ConnectException: Network is unreachable
Downloading: https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma (try 10/10)
Exception: java.net.ConnectException: Network is unreachable
Unable to download remote file. Check your internet connection/proxy settings.
FATAL ERROR: net.minecraft.bootstrap.FatalBootstrapError: Unable to download while being forced
at net.minecraft.bootstrap.Bootstrap.execute(Bootstrap.java:95)
at net.minecraft.bootstrap.Bootstrap.main(Bootstrap.java:381)


Please fix the error and restart.

$ ifconfig
lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 0  (Local Loopback)
        RX packets 57381  bytes 17406141 (16.5 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 57381  bytes 17406141 (16.5 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 fe80::bae8:56ff:fe18:7bf6  prefixlen 64  scopeid 0x20<link>
        inet6 fd0a:3bf5:3521::ab1  prefixlen 128  scopeid 0x0<global>
        inet6 fd0a:3bf5:3521:0:bae8:56ff:fe18:7bf6  prefixlen 64  scopeid 0x0<global>
        inet6 2800:40:7aa:1:bae8:56ff:fe18:7bf6  prefixlen 64  scopeid 0x0<global>
        ether b8:e8:56:18:7b:f6  txqueuelen 1000  (Ethernet)
        RX packets 815334  bytes 513927518 (490.1 MiB)
        RX errors 0  dropped 0  overruns 0  frame 445419
        TX packets 608951  bytes 104791299 (99.9 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 18

Just so you know the network and NAT64 work fine:

$ curl -I https://s3.amazonaws.com/Minecraft.Download/launcher/launcher.pack.lzma
HTTP/1.1 200 OK
x-amz-id-2: UpAM7gl/HRnjvhD21HJj56/NHwQY4JHekomKtVVCDE3wv4Ij//zDBVzbQN3ceugt
x-amz-request-id: D8E156927B40322B
Date: Thu, 05 Jun 2014 15:32:56 GMT
Last-Modified: Mon, 19 May 2014 16:22:49 GMT
ETag: "33b37ac5b5b4842482c27c2499c8b3c7"
Accept-Ranges: bytes
Content-Type: application/octet-stream
Content-Length: 1027461
Server: AmazonS3