Filter: Implement direct recursion

Direct recursion almost worked, just crashed on function signature check.
Split function parsing such that function signature is saved before
function body is processed. Recursive calls are marked so they can be
avoided during f_same() and similar code walking.

Also, include tower of hanoi solver as a test case.

filter/f-inst.h

@@ -22,7 +22,7 @@
 
 /* Flags for instructions */
 enum f_instruction_flags {
-  FIF_PRINTED = 1,		/* FI_PRINT_AND_DIE: message put in buffer */
+  FIF_RECURSIVE = 1,		/* FI_CALL: function is directly recursive */
 } PACKED;
 
 /* Include generated filter instruction declarations */