use the RegisterPlugin function instead of manipulating AvailablePlugins directly, and get rid of the silly plugin_loader.go.in setup.
Move the plugin init into the pipeline package so the tests will still run.
re-add plugin_loader.go to .gitignore since heka-build might generate it.
update install notes to refer to heka-build and better 'go get'
Merge pull request #23 from mozilla-services/features/register-plugins

Features/register plugins