1. expanding_macro global boolean removed. Compiled closures should be used whenever available, even during macro expansion.
2. Closure object passed as parameter to compile_to_c() to make available the closure environment during compilation.
3. Related to #2 above, new function refer1() that deconstructs symbols encountered during compilation by looking at the closure environment.
4. FRAME instruction to be made native instead of just a call to frame(), preparatory work done for this.
5. Simplified closure invocation. If compiled code available, execute it, else compile and execute it.