env: add r5js.IEnvironment#hasClosure as a temp. workaround.
env: r5js.IEnvironment#hasBindingRecursive should never search closures.
env+misc: remove second param from r5js.IEnvironment#hasBindingRecursive.
env: remove r5js.RootEnvironment#setLookaside. Apparently unneeded.
env: transform r5js.RootEnvironment into a useless shell to be removed.
env: use r5js.IEnvironment#isImplementedBy instead of direct instanceof checks.
env+misc: remove r5js.RootEnvironment.