Macro scope nesting

A problem with recursing macros is that scopes are not nested
when "velocimacro.context.localscope" is set to true. That is, a get() on a
context does not percolate to a parent context if the get() returns null. This
prevents accessing global variables in the context. The desired behavior
(IMHO) would be for set()s to be local to the macro, and get()s to percolate up
to the parent if not found.