Adapt to Rhino's NativePromise

[grob]

When directly calling Function objects processMicrotasks must be called before exiting the current context, otherwise pending promises won't be settled (see [1])

Found just two places in Ringo where calling processMicrotasks is necessary, but i might have missed some. Added a very basic test and enabled three other rhino tests that weren't executed by default (dunno why).

[1] https://github.com/mozilla/rhino/blob/master/src/org/mozilla/javascript/Context.java#L2326

[botic]

I found two more JS function calls in Java:

ringojs/src/org/ringojs/engine/ModuleLoader.java

Line 170 in 9bb6a2e

Object source = function.call(cx, scope, scope, args);

ringojs/src/org/ringojs/util/ScriptUtils.java

Line 196 in 9bb6a2e

function.call(cx, scope, thisObj, args);

But not sure if this should trigger also the microtask queue.