Add decorator for caching function results.

[SVN r64350]

src/util/__init__.py

@@ -1,4 +1,5 @@
 
+# Decorator the specifies bjam-side prototype for a Python function
 def bjam_signature(s):
 
     def wrap(f):       
@@ -6,3 +7,23 @@ def bjam_signature(s):
         return f
 
     return wrap
+
+class cached(object):
+
+    def __init__(self, function):
+        self.function = function
+        self.cache = {}
+
+    def __call__(self, *args):
+        try:
+            return self.cache[args]
+        except KeyError:
+            v = self.function(*args)
+            self.cache[args] = v
+            return v    
+
+def unquote(s):
+    if s and s[0] == '"' and s[-1] == '"':
+        return s[1:-1]
+    else:
+        return s