Add ICMP tests to travis-ci (refactored exclusions to work
with rvmsudo);
Drop ruby 1.8.7 test;
Fix ping of 192.168.0.1 to use 127.0.0.1 instead;
Move handling of EXCLUDE_ICMP_TEST to the same place as other excludes;
Add to Known Issues in README based on testing results
Merge pull request #31 from ianheggie/add_icmp_tests_to_travis

Add icmp tests to travis, drop ruby 1.8.7, note known issues discovered in testing