Updated gemspec to add check for signing key so that we can also build unsigned gem.
Add travis ruby 2.0.0 and rubinius 1.9 tests back to travis configuration while initially allowing failures for both new rubies in order to not interrupt the build.
Add travis build status image to README.rdoc.
Merge remote-tracking branch 'origin/add-travis-configuration' into integration

Conflicts:
	README.rdoc
	memcached.gemspec