Minor changes to assist with minification
Added 'flag' and 'unflag' methods
Replaced use of "Array.slice" to convert arguments to array with our own function, which is much faster!

Changed name of "_events" property to "_listeners", added underscores to other properties that we add (so it will be easier to minify these names later)
Moved code to check if emitter is compacted from tests to within emitter itself