backend/udp: If either tun or udp get read optimistically repeat

This optimization bypasses poll() under continuous activity like
bulk transfers.  In simple dd | ncat tests this change eliminated
practically all poll() calls during the transfer, substituting them
with EAGAIN read()/recvfrom() calls at half the original poll()
occurrences.

The ctl fd is intentionall starved by this change, and an upper
bound could be placed on how long we do so by adding a simple
counter to break the inner loop if necessary.
Merge pull request #86 from vcaputo/udp_optimistic_reads

backend/udp: If either tun or udp get read optimistically repeat
bug fix: LeaseAttrs lost on lease-renew
Merge pull request #89 from eyakubovich/master

bug fix: LeaseAttrs lost on lease-renew
iptables: support iptables older than 1.4.11

this checks the version of iptables, if it's older it'll use an iptables list
command to check if a rule exists, otherwise it'll use the newer -C command

Fixes #91
Merge pull request #92 from mindscratch/issue-91-support-old-iptables

iptables: support iptables older than 1.4.11
Prefer global instead link-local iface addr

Some environments may assign multiple IP addresses
on a single interface. It's better to use a global
address to a link-local one (which was probably used
for bootstrapping).

Fixes #73
Add support for TLS between flannel and etcd

Fixes #63
Merge pull request #96 from eyakubovich/tls

Add support for TLS between flannel and etcd
Bug fix: base64 encoded data appeared in lease attrs

For some reason, json.Marshal'ing struct (vs ptr to it)
has odd interaction with json.RawMessage.

Fixes #97
Merge pull request #94 from eyakubovich/link-local

Prefer global instead link-local iface addr
Merge pull request #99 from eyakubovich/base64-bug

Bug fix: base64 encoded data appeared in lease attrs
Top-level Dockerfile will build using golang:onbuild

dist/build-docker has been added to produce images
based on flannelbox.

Fixes #75
Merge pull request #100 from eyakubovich/flannel-git

Top-level Dockerfile will build using golang:onbuild
Update -etcd-endpoints command line option in README

This patch updates the "key command line options" section in the README to reflect the changes regarding -etcd-endpoint(s) made in 74f9413deb00c0ca01bfb217aa56717b6edcfe64
Merge pull request #104 from patrickhoefler/feature/fix_etcd-endpoints_in_readme

Update -etcd-endpoints command line option in README
bump to v0.2.0
bump to 0.2.0+git
Merge pull request #106 from eyakubovich/master

version bump
Add new "routed" backend.

Add a new "routed" backend that forwards traffic using regular IP
routes.  Useful on private layer2 networks (or dedicated virtual
networks).