nested OSC bundle support for scsynth (issue #776)

A patch to introduce support for nested OSC bundles to scsynth (as part of issue #776).

I've taken the simplest approach to implement nested OSC bundles by using the existent infrastructure by means of a simple recursive function call when a nested bundle has been found.

By doing so, only bundles on the first nesting level of a root bundle will be scheduled (if requested so by the timetag). But this is fine according to the spec, as it says the following about scheduling of multi-level nested bundles:

"When bundles contain other bundles, the OSC Time Tag of the enclosed bundle must be greater than or equal to the OSC Time Tag of the enclosing bundle."