Add notes about specific release branches.
adjust regex for finding mininet's links during cleanup

link names of the form "a-b-ethN" were previously interpreted
as "b-ethN". this change accepts link names with a dash, and
requires N to only contain digits.
Canonicalize dpid by removing colons and padding with zeros
closes #268
Merge pull request #263 from adferguson/clean-fix

adjust regex for finding mininet's links during cleanup
Merge pull request #258 from ggee/MininetINSTALL

Add notes about specific release branches.