Fix $$ escaping.

Squashed commit of the following:

commit ef1a217b
Author: Romain Courteaud <romain@nexedi.com>
Date:   Tue Oct 11 10:01:10 2011 +0200

    Escape $$ character to $.

    Do not escape when fetching dependency values.

commit 8232c9aa
Author: Antoine Catton <acatton@tiolive.com>
Date:   Mon Oct 10 09:57:12 2011 +0200

    Add tests for dollar sign escaping

src/zc/buildout/buildout.py

@@ -1295,6 +1295,7 @@ class Options(UserDict.DictMixin):
         self._raw = data
         self._cooked = {}
         self._data = {}
+        self._non_escaped_data = {}
 
     def _initialize(self):
         name = self.name
@@ -1356,11 +1357,17 @@ class Options(UserDict.DictMixin):
         v = '$$'.join([self._sub(s, seen) for s in v.split('$$')])
         self._cooked[option] = v
 
-    def get(self, option, default=None, seen=None):
+    def get(self, option, default=None, seen=None, escaped=True):
+        if escaped:
             try:
                 return self._data[option]
             except KeyError:
                 pass
+        else:
+            try:
+                return self._non_escaped_data[option]
+            except KeyError:
+                pass
 
         v = self._cooked.get(option)
         if v is None:
@@ -1383,8 +1390,13 @@ class Options(UserDict.DictMixin):
             v = '$$'.join([self._sub(s, seen) for s in v.split('$$')])
             seen.pop()
 
+        self._non_escaped_data[option] = v
+        v = v.replace('$${', '${')
         self._data[option] = v
-        return v
+        if escaped:
+            return self._data[option]
+        else:
+            return self._non_escaped_data[option]
 
     _template_split = re.compile('([$]{[^}]*})').split
     _simple = re.compile('[-a-zA-Z0-9 ._]+$').match
@@ -1417,7 +1429,8 @@ class Options(UserDict.DictMixin):
             section, option = s
             if not section:
                 section = self.name
-            v = self.buildout[section].get(option, None, seen)
+            v = self.buildout[section].get(option, None, seen,
+                                           escaped=False)
             if v is None:
                 if option == '_buildout_section_name_':
                     v = self.name

src/zc/buildout/tests.py

@@ -3587,6 +3587,73 @@ def increment_on_command_line():
       recipe='zc.buildout:debug'
     """
 
+def bug_664539_simple_buildout():
+  r"""
+  >>> write('buildout.cfg', '''
+  ... [buildout]
+  ... parts = escape
+  ...
+  ... [escape]
+  ... recipe = zc.buildout:debug
+  ... foo = $${nonexistent:option}
+  ... ''')
+
+  >>> print system(buildout),
+  Installing escape.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  """
+
+def bug_664539_reference():
+  r"""
+  >>> write('buildout.cfg', '''
+  ... [buildout]
+  ... parts = escape
+  ...
+  ... [escape]
+  ... recipe = zc.buildout:debug
+  ... foo = ${:bar}
+  ... bar = $${nonexistent:option}
+  ... ''')
+
+  >>> print system(buildout),
+  Installing escape.
+    bar='${nonexistent:option}'
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  """
+
+def bug_664539_complex_buildout():
+  r"""
+  >>> write('buildout.cfg', '''
+  ... [buildout]
+  ... parts = escape
+  ...
+  ... [escape]
+  ... recipe = zc.buildout:debug
+  ... foo = ${level1:foo}
+  ...
+  ... [level1]
+  ... recipe = zc.buildout:debug
+  ... foo = ${level2:foo}
+  ...
+  ... [level2]
+  ... recipe = zc.buildout:debug
+  ... foo = $${nonexistent:option}
+  ... ''')
+
+  >>> print system(buildout),
+  Installing level2.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  Installing level1.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  Installing escape.
+    foo='${nonexistent:option}'
+    recipe='zc.buildout:debug'
+  """
+
 ######################################################################
 
 def make_py_with_system_install(make_py, sample_eggs):