checking in initial weekend's work

compile.py: ASTVisitor framework plus bits of a code generator that
    should be bug-for-buf compatible with compile.c

misc.py: Set and Stack helpers

test.py: a bit of simple sample code that compile.py will work on

Lib/compiler/misc.py

+class Set:
+    def __init__(self):
+	self.elts = {}
+    def add(self, elt):
+	self.elts[elt] = elt
+    def items(self):
+	return self.elts.keys()
+    def has_elt(self, elt):
+	return self.elts.has_key(elt)
+
+class Stack:
+    def __init__(self):
+	self.stack = []
+	self.pop = self.stack.pop
+    def push(self, elt):
+	self.stack.append(elt)
+    def top(self):
+	return self.stack[-1]

Tools/compiler/compiler/misc.py

+class Set:
+    def __init__(self):
+	self.elts = {}
+    def add(self, elt):
+	self.elts[elt] = elt
+    def items(self):
+	return self.elts.keys()
+    def has_elt(self, elt):
+	return self.elts.has_key(elt)
+
+class Stack:
+    def __init__(self):
+	self.stack = []
+	self.pop = self.stack.pop
+    def push(self, elt):
+	self.stack.append(elt)
+    def top(self):
+	return self.stack[-1]