Empty function bodies
Fix closure returning invalid stack value.

When a closure has a single expression followed by a ";", it emits a
"pop" at the end of the instruction, followed by a "return_top", thus
messing up the stack. The provisional (and confusing) fix is to
"return_null" at the end of the expression followed by a ";".
Fixing toplevel lookup with env
Using 'this' from ep when appropriated
Fixing jump offset
memetest.mm working.

-Fixed binding of `e` in "catch(e)"
-Fixed Exception.toString: making sure it always returns a string
-Compiling a list of files passed as arguments in the shell
-Improved Makefile
Fixing label clash for 1+ closures in scope
Porting old tests